I have a timesheet in Excel, and users have the ability to work more
than their contractual hours each week. These 'additonal' hours, can
then be used to leave work early, start late etc. So, I may have an
entry as follows showing the total number of hours worked in a week:

Monday 09:05
Tuesday 09:05
Wednesday 08:50
Thursday 07:20
Friday 06:35

This should show a cumulative total of 03:55, showing that the person
has worked 03:55 more than their contractual hours. If the following
week, they show the following times:

Monday 07:00
Tuesday 07:50
Wednesday 07:20
Thursday 07:20
Friday 07:00

This would show that they were down 00:30 on the week but
cumulatively, they were up 03:25.

Can anyone help with this calculation?

Many TIA

Duncs