Microsoft Project calendars – How accurately do working times have to be set?

Here’s a question that crops up a lot:

The calendars in Microsoft Project are set up by default to show an 8 hour day, starting at 8:00am and finishing at 5:00pm, with a break of 1 hour between 12:00pm and 1:00pm. Our company has a 38 hour week, with each working day being 7.6 hours per day, which works out to 7 hours and 36 minutes per day. What’s the best way to modify the calendars in Microsoft Project to reflect this? By the way, our calendar has already been updated with all relevant public holidays such as Christmas Day, Boxing Day and so on.

The warning bells start ringing when I hear questions like this, as in most cases it means that Microsoft Project users are in the process of making an easy job unnecessarily difficult. A couple of questions will sort out if any of this detailed calendar work is needed.

The first question we ask is “what’s the shortest duration of your average task?” Aside from milestones, which have a duration of 0, we find that the average Microsoft Project user will have minimum durations of 1 day, or possibly half a day. Sometimes we see minimum task durations of 2 hours, but on balance, tasks that have been assigned a duration this short may be underestimated.

That’s a problem within itself, and we’ll talk about that in a separate post.

If you’ve correctly estimated your shortest task durations to be either half a day or 1 day, the reality is that you’re probably only interested in Microsoft Project indicating on which day you are scheduled to perform a task, or whether it’s to start in the morning or afternoon. It’s unlikely that you’d ever want Project to tell you that your task is scheduled to start at exactly 2:43pm, for example. In most cases, that’s not useful information.

When you’re discussing slippage (how late a task started/finished versus where it was projected to start/finish), you’re more likely to say “we should have started on Monday 23rd March, but we wound up starting on Thursday 26th March because Fred accidentally destroyed the forklift”. You’re less likely to say “we should have started at 2:25pm on Monday but would up starting at 3:45 on Thursday”.

There’s an exception to this, which brings up the second question: “are you tracking the work performed during tasks.”

Some clients do. Many software developers, to use one example, want to keep detailed track of how much work was scheduled and how much work was performed. They might bill their clients in increments of 10 minutes, so that sort of detail is reasonable. But it’s also unusual. I’d estimate that less than 5% of our clients have any interest in scheduling or recording actual work.

So, to make a long story short, if you’re not interested in that level of detail, we recommend that you leave your calendars at the default 8 hours. In terms of your ability to schedule effectively, it won’t make any difference. Of course, remember to put your non-working days in as exceptions.

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