5-2-2 Default overime over 40 hrs per week

I have always calculated OT manually.  Now I see that under options, you can check the box so the system will do this.

So, this week, i did that, and when i look at the timesheets (after final calcuations) it doesn't show any of the hours being moved into OT.

How exactly, do I get this to work?

Thank you.

Deborah