Primavera P6 has the capability to model either workday or 24-hour elapsed time lags in your schedule. A 24-hour elapsed time lag can be very useful when you are trying to model such constants as the cure process for concrete, which of course doesn’t take the weekend off like its surrounding activities.
Primavera P6 Example
As an example, let’s say you have a construction project that requires the installation of several concrete structures. Figure 1 displays a sample section of that schedule, and clearly shows the concrete installation process. Note that your Pour Concrete task currently has zero lag, Figure 1.
Again, as displayed in Figure 1, all the tasks use the standard Finish-to-Start relationship. This works well for the sequential nature of the project. The only outstanding issue is that you want to accurately describe in your schedule a 5-day “round the clock” cure time delay from the time your concrete is poured to the time it is cured, and the forms can be removed.
How should your schedule account for this concrete cure time delay?
This article describes how to add lag to the classic Finish-to-Start relationship to describe cure time delays.
Selecting a 24-hour Lag Calendar
The first step in scheduling the cure time delay is to select the schedule icon from the P6 Professional tools group at the top of the screen, Figure 1. You may also select Tools | Schedule from the top drop down menu. Next click the Options button in the Schedule dialog box, Figure 2.
At the very bottom of the Schedule Options: General tab menu is the drop-down menu “Calendar for scheduling Relationship Lag”. Select the “24 Hour Calendar” from this drop down menu, Figure 3.
Entering you Concrete Cure Time Lag
Now you are almost ready to enter your concrete cure time lag.
Before entering the Lag for the task “C – Pour Concrete” first note your project calendar, which is viewed by selecting General from the bottom details view. For our example we are using the Corporate – Standard Full Time calendar, which is your standard 5-day, 8-hour work week calendar.
Select Activity Name “D – Strike Forms” from the list of task, and then select the Predecessors tab from the bottom details view. The Lag column, Figure 4, is where you will enter your Lag time.
Here it is easiest to enter the total length of your concrete cure lag time in hours. Our cure Lag is 5-days, so 5-days times 24-hours for each day comes to a total Lag time of 120-hours. Enter “120h” in the Lag column. Figure 4, and Primavera P6 will automatically calculate your Lag time in days, which for our example comes to 15-days, Figure 5.
Wait a minute! Fifteen days is a long time. I thought our cure time Lag was only 5-days? It is, but for our project standard 5-day calendar Primavera P6 considers each block of 8-hours in our 24-hour Calendar for scheduling Relationship Lag as 1-day. So each 24-hour period of time will be 3-days Lag. Our 5-day cure time comes to a 15-days Lag, using the 24-hour Calendar for Relationship Lag and the standard 8-hour a day project schedule.
Again, if this seems confusing, simply enter your total cure time in hours and let Primavera P6 compute the Lag time in days for you.
For our example, schedule your project by selecting the Schedule button. Your project Gantt chart with the 5-day “anytime” cure time delay will be as displayed in Figure 5.
Entering a cure time delay is probably a little more complex than you would like, but it’s worth the extra step in case an activity slips and a weekend falls between the two activities. If that happens, you’ll have an inaccurate lag using the other options. However, you can take the confusion out of the equation by simply entering the total Lag cure time in total hours, and let Primavera P6 compute the equivalent cure time in days.
One more point to note is that, once selected, Primavera P6 will use the 24-hour “Calendar for scheduling Relationship Lag” for all your lags in the schedule. So if you have a 4-day business day delivery lag in addition to a cure time lag you will have to find another way to describe that delivery delay lag, the “24-Hour Calendar” for Lag will not do.
For the delivery delay, perhaps, you could simply create a four day acquire parts task that has no resource assignments, and, therefore, no associated cost.