Hi,

today I’m going to show relation between Fixed Duration Task Type, and Overtime Work in MS PROJECT 2016.

First I’m going to create a simple Project with one Task – Fixed Duration:

As you can see In the Gant Chart I added Type Column! Now I will assign john as Resource to this Task:

Now I will switch to the Task Usage View, and I will show Task Form:

As you can see on the right part of this View, I’ve added Ovt. Work. If you do not know how to get it it is described in my post from 10/7/2017.

Now I will put 8 hours in Ovt. Work field, and I will click at OK button:

and I will get:

Why 12 hours/day? 24 hours of total work – 8 hours of overtime work is 16 hours. 16 hours divided by 8 hours regular work per day is 2 days. And John will work 8 hours each day (regular work) and (8 hours of total overtime / 2 days) = 4 overtime hours per day. So, 8 + 4 = 12. 
BUT! Since I have Fixed Duration Task Type, Duration still remains 3 days even John is not going to work at the third day. Why is it so? It seems unreasonable, but it is not. What if I add Mary at the Task now? And she is not suppose to work overtime. I will get:

Since I have Fixed Duration = 3 days, MS PROJECT knows that Mary should work three days, and those 24 hours are divided in those three days. If  duration was changed to two days after I put Overtime Work for John, Mary will have to work only 16 hours, and that is not correct, because I have 3 day Fixed Duration Task. Keep that in mind before you think that that this is bug!

Regards