project time management ashima wadhwa. schedule development – determining start and finish dates...

Project Time Management

Ashima Wadhwa

Schedule Development

– Determining start and finish dates for project activities

– Without realistic dates, project unlikely to be finished as scheduled

– Schedule development process often iterates as more information becomes available (process inputs)

Schedule Development Inputs:

– Project Network Diagram– Activity Duration Estimates– Resource Requirements– Resource Pool Description – availability patterns; shared

resources are highly variable– Calendars – define eligible work periods

• Project Calendars affect all resources• Resource Calendars – affect specific resource pools or individuals

Schedule Development Inputs (continued):

– Constraints• Imposed Dates – may be required• Key events or milestones – are initially requested and become

expected during project

– Assumptions– Lead and Lag Time – dependencies may specify time in

order to satisfy relationship (example – 2 weeks to receive order)

Schedule Development Tools & Techniques

• Mathematical Analysis• Monte Carlo Analysis

Mathematical Analysis

– Mathematical Analysis – calculating theoretical early/late finish and start dates without regard for resource pool limitations; indicate time periods which activity should be scheduled given resource limits and other constraints:• Critical Path Method (CPM) – single early/late start and finish date for all activities.

Based on specified, sequential network and single duration estimate. Calculates float to determine flexibility

• Graphical Evaluation and Review Technique (GERT) – probabilistic treatment of network and activity duration estimates

• Program Evaluation and Review Technique (PERT)- sequential network and weighted average duration to calculate project duration – differs from CPM by using mean (expected value) instead of most-likely estimate in CPM

Mathematical Analysis

– Critical Path Method: refers to estimating based on one time estimate per activity• One time estimate per task (Most Likely)• Emphasis on controlling cost and leaving schedule flexible• Drawn using AOA diagrams• Can have dummy task

– PERT (Program Review and Estimating Technique)• 3 Time estimates per activity

– Optimistic– Pessimistic– Most Likely

• Emphasis on meeting schedule, flexibility with costs• Drawn on AOA diagrams• Can have dummy tasks

Monte Carlo Analysis

– Monte Carlo Analysis• Uses a computer with PERT values and network diagram• Tells

– Probability of completing a project on any specific day– Probability of completing a project for any specific amount of cost– Probability of any task actually being on the critical path– Overall Project Risk

• Suggests that Monte Carlo simulation will create a project duration that is closer to reality than CPM or PERT


• Schedule Development Tools & Techniques (continued)– Duration Compression – look to shorten project schedule

without affecting scope• Crashing – cost and schedule trade-offs to determine greatest

amount of compression for least incremental cost – often results in higher costs

• Fast Tracking – performing activities in parallel that normally would be sequenced – often results in re-work and usually increases risk

– Simulation


• Schedule Development Tools & Techniques (continued)– Resource Leveling Heuristics – leveling resources that

apply to critical path activities a.k.a. “resource constrained scheduling” – when limitation on quantity of available resources; sometimes called “Resource Based Method” – often increases project duration

– Project Management Software

Chapter 6 – Project Time Management

• Schedule Development Tools & Techniques (continued)– Project Manger’s role

• Provide the team with the necessary information to properly estimate the task

• Complete a sanity check of the estimate• Formulate a reserve

– Project Team should be involved; determine task estimates• Historical Records• Guesses• Actual Costs • Benchmarks• CPM and PERT

Critical Path Method:

– Critical Path Method: longest path through a network diagram and determines the earliest completion of the project

– Proves how long the project will take– Indicates tasks that need most monitoring– Almost always have no slack

Schedule Development Outputs:

– Project Schedule – includes planned start and finish dates for each activity; remains preliminary until resources assignments are approved. Usually in following formats:• Project Network Diagrams (with date information added) – show

logical and critical path activities• Bar or Gantt charts – activity start and end dates, expected

durations• Milestone Charts – identifies key deliverables and interfaces • Time-scaled network diagrams – blend of project network and bar

charts


• Schedule Development Outputs (continued):– Supporting Detail – all assumptions and constraints. May

also include:• Resource requirement by time period (resource histogram)• Alternative schedules (best/worst case)• Schedule reserve/risk assessments

– Schedule Management Plan – how updates are managed– Resource requirement updates – leveling and activity

impact


• Schedule Control:– Influencing factors which create schedule changes to

ensure changes are beneficial– Determining that schedule has changed– Managing actual changes as they occur

• Inputs to Schedule Control– Project Schedule – baseline approved, measure against

project performance– Performance Reports – planned dates met, issues– Change Requests– Schedule Management Plan


• Schedule Control Tools & Techniques– Schedule Change Control System – defines

procedures for schedule changes, paperwork, approval, tracking systems

– Performance Measurement – assess magnitude of variations to baseline; determine if corrective action is needed

– Additional Planning – Project Management Software

Schedule Control Outputs:

– Schedule Updates – any modifications, stakeholder notification• Revisions change scheduled start and finish dates –

generally in response to scope changes. “Re-baselining” may be needed in drastic situations

– Corrective Action – re-align performance with project plan

– Lessons Learned


• Key knowledge points not in PMBOK– Need to know manual calculations of network

diagrams• Created after project charter and WBS (task estimates

and dependencies are determined)– Mandatory dependencies (Hard Logic) – inherent in nature of

work– Discretionary dependencies (Soft Logic) – based on

experience, desire or results– External dependencies – based on needs and desires of

organizations outside the project


• Methods to draw network diagrams– Activity on Node (AON) or Precedence Diagramming

Method (PDM)• Boxes represent tasks• Arrows show task dependencies• 4 types of task relationships

– Finish to Start (task must finish before next can start)– Finish to Finish (task must finish before next can finish)– Start to Start (task must start before next can start)– Start to Finish (task must start before the next can finish)

• No dummy tasks used


• Methods to draw network diagrams– Activity on Arrow (AOA or Arrow Diagramming Method

(ADM)• Arrows used to represent tasks• Only Finish to Start relationships are used• May use dummy tasks (show dependencies)• PERT and CPM estimating techniques can only be drawn using

AOA– CPM (Critical Path Method) – estimating based on one time estimate

per activity (the most likely time estimate)» Emphasizes controlling cost and allowing schedule flexibility» Can have dummy tasks


• Methods to draw network diagrams– Activity on Arrow (AOA or Arrow Diagramming

Method (ADM) continued:• PERT (Program Evaluation and Review technique)

– 3 time estimates per activity: Optimistic (O), Most Likely (M), Pessimistic (P)

– Emphasizes meeting schedule, flexibility with cost– Can have dummy tasks


• Methods to draw network diagrams– PERT (Program Evaluation and Review technique)– Estimating based on 3 formulas:

• PERT Duration: (P + 4M + O)/6• Standard Task Deviation: (P – O)/6• Task Variance:

• Total project estimate:– Add up all Optimistic, Most Likely and Pessimistic values of the critical path

tasks and apply P + 4M + O/6 • Total project variance (+/-):

– Add up the individual task variances and take the square root of the value. Use the value as a +/- figure to compute the Optimistic and Pessimistic values. The total project estimate will serve as the basis.

[P – O]2

6


• Monte Carlo Simulation:– Uses a computer with PERT values (P, M, O) and a network

diagram but does not use the PERT formula– Indicates

• Probability of completing project on a specific day• Probability of completing project for any specific amount of cost• Probability of any task actually being on critical path• Overall project risk


• Estimating techniques in general:– Should be performed by entire project team

• Project manager needs to provide information to allow team to create estimates; sanity check; formulate reserve

– Estimates are:• Guesses, Historical Records, Actual Costs, Benchmarks, CPM, PERT

– Critical paths determines the earliest completion date and identifies tasks that need monitoring

– Can be obtained by CPM, PERT and Monte Carlo estimating techniques


• Key Definitions:– Slack (Float): the amount of time a task can be delayed

without delaying the entire project. Tasks on critical path have no slack. • Slack is calculated by the difference between Early Start and Late

Start of a task– Free Slack (Float): the amount of time a task can be delayed without

delaying the early start date of its successor– Total Slack (Float): the amount of time a task can be delayed without

delaying the project completion date

– Lag: inserted waiting time between tasks


• General Comments:– Projects can have more than 1 critical path (increases risk) and can

involve dummy tasks– Negative float indicates that you are behind– Resource Leveling involves possibly letting schedule and cost slip– Heuristics – just means “rule of thumb” e.g. 80/20 rule– Schedules are calendar based – makes this different than a time

estimate• Bar Chart a.k.a. Gantt chart (track progress, report to entire team

including stakeholders, control tool)• Network Diagram (to show task inter-dependencies, show project

organization, basis for project control)• Milestone chart (report to Senior management, shows major events)

• General Comments:– To shorten project schedule examine the critical

path• Crashing – add more resources to the critical path tasks

– Usually results in increased cost• Fast Tracking – performing tasks in parallel

– Can result in re-work and increased risk– Best to select method that has least impact on the

project (is the importance on cost, risk or schedule?)


• General Comments:– Bar (Gantt) Charts

• Weak Planning Tool, effective progress and reporting tool• Does not show interdependencies of tasks• Does not help organize the project more effectively

– Network Diagrams (PERT, CPM, PDM)• Shows task interdependencies• Aids in effectively planning and organizing work• Provides a basis for project control

– Milestone Charts• Only shows major events• Good for reporting to management and customer

– Flow Charts• Depicts workflow and not commonly used for project management


• General Comments:– Free Slack (Float) – amount of time a task can be delayed without delaying the early start

date of its successor– Total Slack (Float) – amount of time a task can be delayed without delaying the project

completion date

• Lag – inserted waiting time between tasks• Resource Leveling – level peaks of resource usage; stable number of resources –

allows schedule and cost slip in favor of leveling resources• Heuristic – rule of thumb (80/20 rule)

project time management ashima wadhwa. schedule development – determining start and finish dates...

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