I am creating a daily timesheet

A1 = time started (08:00)
B1 = time ended
C1= total hours worked - I am fine up to this point

Now I want to calculate:
D1 to be regular hours worked <= 8 hrs
E1 to be overtime hours > 8 hrs, < 12 hrs
F1 to be double time hours >= 12 hrs

I am just lost - I have been searching for 4 hours and am more confused re ((, IF
I'd appreciate any help. Thanks