Difference between hours

Hey,
I need to think about working hours of a garage worker
For example:
Start time : 10:10
Finish time: 10:30
If i do finish time minus start time I get in my output 0 and i want to get : 20 min
or 20/60 = 0.33 hours
how can i do it ?

Difference between hours.rp (47.8 KB)