How about showing readers some sample data and your sample calculations?
Why do you want to store 1 hour duration as 1:00??
Isn't it really 1 hour - not 1 o'clock.
Code:
1 hour = 60 minutes
If you work 1 hour, then 20 minutes, your total time of work would be calculated as follows:
--day 1 ---- 1 hour
--day 2 ---- 20 minutes
You need to get common units of measure
1 hour = 60 minutes
so day 1 --------------- 1 hour or 60 minutes
day 2 --------------------------- 20 minutes
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Total time worked ( in minutes) 80