Hi I am new to project 2013. I met a problem when using recurring task function:

I have several tasks ongoing at the same time, one of them is spending 2 hours per day to check the data quality.
I set up a recurring task, select the start date, and set the end end point as 'after 20 occurance'.

I assume that the task should last for 20 working days, however, the summary of recurring task count the duration as 19.25 days.
I don't know how it is calculated. What's more, when I allocate myself to other tasks, it always shows that I am overallocated in
the recurring task.

I want the duration to be 20 days and I also want to allocate me to other tasks during the period. I thought maybe resetting the task mode of
the recurring task is a solution. Can anyone help me to fix the problem?

Any help would be appreciated! Thanks a lot!