Tasks like “concrete curing” and “process testing” that take place 24 hours per day are sometimes referred to as “Elapsed Duration Tasks” and may be modeled in a number of different ways.
One option is to put the elapsed duration task on a 24 hour per day 7 day per week calendar but this is not recommended with Microsoft Project as this will result in incorrect calculation of the task and float durations in days.
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Microsoft Project users should consider using the “Elapsed Duration” function to model tasks working 24 hour per day if they wish to assign a 24×7 calendar to a task because the duration is days is displayed correctly, but this option will result in losing the critical path on the “elapsed” duration tasks.
The disadvantage of making a Microsoft Project task “Elapsed” is that if the predecessor ends at 17:00 then a 5-day curing activity will start and finish at 17:00 and will have float when the successor starts the following morning.
Managing Elapsed Duration Tasks in Microsoft Project
To reduce the loss of the critical path I recommend putting elapsed duration tasks on calendars with the same hours per day as the other work, but on a 7 day/week basis without weekends or non-workdays. Therefore, when the curing activity ends on Friday or Saturday evening, then it will normally still have Total Float when the successor may not start till the following Monday, so this technique will not solve the issue of losing a critical path in all circumstances.
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Paul E Harris
Director Eastwood Harris Pty Ltd
11 December 2023