System calculation for 'Earliest finish time' in maintenance order operation

Hi,

Please help me to figure out how SAP calculates the 'Earliest fininsh time' in maintenance order opeartion. refer below screenshot:

For operation 'test', I have entered 10 mins as work required, as per me the earliest finish time should be 08:10:00 instead 08:07:30.

I wonder from where the calculation is coming?

Thanks.

-Lucky.