The schedule model development approach includes tasks such as:

Selecting data for:

• Creating activities
• Resources
• Calendars
• Work Breakdown Structure (WBS)
• Milestones
• Lags
• Dependencies
• Activity duration

This data can be gathered in team meetings, BoQs (Bill of quantity), etc.  

Further, we also choose:

• Schedule model presentation forms e.g. Gantt Chart, table, milestones, network diagram, simple list.
• Schedule life cycle type. Schedule Life cycles are explained here.

Various sources can be referred to for help when defining schedule development approach, explained here.

Activities are work to be performed. The project activities have the following characteristics:

Activity owner: a single person accountable for its performance. That person also reports progress on the activity.

Activity description: Name like ‘pour wall’ is self explanatory but some detail should be added such as ‘pour the east wall from top to bottom’.

Continuity of activity: Activity should represent continuous work. If any break to be added in activity, it is better to split the activity from breakpoints. 

Activity Start and Finish dates.

Activity Duration: Ideally, activity duration should be less than two times the update cycle. For example schedule is updated after every 10 days. The activity duration should be 5 or less. 

• This is to allow reporting of the start and finish of the activity within one or two update cycles. 
• This helps the management to focus on performance.
• This is not applicable on Summary, Level-of-Effort (LoE) and Hammock activities.

What is the role of a scheduler? Scheduler performs many tasks. The tasks he will do will be assigned to him by a project manager. His tasks could include:

• Gathering schedule data (milestones, activities and their attributes e.g. dates, except risk activities)
  
  
• Attending meetings to discuss schedule, format, reporting format.
  
  
• Revising schedule.
  
  
• Update plan with actual progress of activities, resources productivity rates.
  
  
• Analysis of plan and actual progress.
  
  
• Analyzing critical path
  
  
• Perform resource leveling
  
  
• Creating reports of plan, actual and forecasted schedule.
  
  
• Creating Work Breakdown Structure (WBS)
  
  
• Creating Organizational Breakdown Structure (OBS)
  
  
• Creating Resource Breakdown Structure (RBS)

Analogous estimation technique:

It is a comparison technique where we look at a similar activity performed before. If more data is available, the better the estimate will be.

Parametric estimation technique:

Parameters from previous similar activity is taken. E.g. Previous activity took 5 days and it had 3 resources working on it, 10 hours daily. This method is more accurate then analogous estimation

Three-point estimation technique

It is used when there is a great deal of uncertainty about duration. We use these parameters and use in the formulas below.

M = most likely | O = optimistic | P = pessimistic | E = expected duration

• Triangular Distribution:       E = (P + M+ O) / 3
• Beta Distribution (also called PERT - Program evaluation and review technique):      E = (P + M(4) + O) / 6

Beta Distribution is preferred in cases where we have a lot of historical data.  When there is no historic data, only with guesses, use Triangle Distribution.

Using these duration estimation techniques, you can get near-to-accurate duration value. It is much better than just guessing a wrong duration, which will negatively effect the project end date