The system doesn't understand overnight shifts very well. You can get a better idea of how it works if you look at your time card on mytime at the store. You'll see how the system needs to split it up into separate days, even if it's the same shift.
Like if you worked 10pm to 3am each day so far this week, your time card would show:
Sunday
10pm
12am
Monday
12am
3am
---
10pm
12am
Tuesday
12am
3am
---
10pm
12am
Wednesday
12am
3am