Scheduling: Ten Things to Get Right, A Series

No.4 Setting Accurate Durations.

Activities in the schedule should accurately reflect the amount of time they will take to accomplish.

When determining the duration of activities in the schedule, the same rationale and methodology should be used to determine the Cost associated with the activities. Activity durations should be short and meaningful.

Ideally an activities duration will not exceed the update period. For activities that are longer than the reporting period there should be at least one measurable event within that reporting period for the activity for example if I have a four week activity in my updates happened every two weeks then I should have three activities to represent that four week duration. A 2 week activity some kind of checkpoint in the middle and then another two week activity to Capture the remaining duration.

When estimating durations is important to remember that having activity durations that are realistic is important for forecasting program delivery dates and ensuring critical paths are reliable. I keep normal working conditions in mind when estimating durations for activities. Activities with optimum success oriented durations often lead to delays in the schedule. When using the normal condition standard for estimating your time it's gonna take to complete the activities it limits the amount of contingency built into the activities themselves. The best source of durations for the activities is going to be the people executing the activities. They will often have prior experience and knowledge that they can flush out the duration with and give you a more accurate estimate of the time it will take to accomplish the activity.

It's important to note however that oftentimes in early schedule planning those executing the activities will be unavailable. In these situations it's important to rely on historical data and subject matter experts in the field to get reliable early durations for activities in the schedule.

Schedules with very short durations of one day or less will usually imply that the schedule is inaccurate and needs to be updated more than necessary. However, there are certain areas that P6 is used where durations of less than a day are valid. In the turn around and maintenance world for instance where you work around the clock 24 hours a day seven days a week and you update your schedule on a shift by shift basis your durations for activities can be as short as an hour.

Activities that have no direct impact on the project schedule or any of the work being accomplished are usually there for cost tracking purposes of supervisory personnel. These level of effort activities are tied to the start of a sequence and the end of a sequence for whatever that activity needs to support. Oftentimes level of effort activities are used for supervision and overhead to have an accurate accounting of the cost associated with the project.

Activities that Encompass planning activities will normally have longer durations than the discrete activities that they'll be broken down into later. These planning packages or longer activities should be worked into the network logic. Any and all assumptions made too activity duration estimates should be documented in detail. The details should describe the methodology used to create the estimate from duration such as some kind of analysis or subject matter expert opinion.

It's also important to remember that activity duration estimates for WBS elements should be clearly mapped to the corresponding cost estimates in the cost breakdown structure. These two are married and should not be separated.

I often use my cost breakdown structure to construct my work breakdown structure.

Duration Estimates are the backbone of any schedule. The more time and effort we can put into the accuracy of the durations the better our schedule will be as long as our logic is correct. Perfectly accurate activity durations do not guarantee schedule success because, logic can change and things hardly ever go according to plan.