It's basically simple:

Example 1:
Leader clocks 52h26'09"
Second clocks 52h27'21"

How to find out the difference for every other rider?

Whenever I try to enter this times I end up with a date...

Example 2:
Leader: Accum. time: 52h26'09"
Next stage: 4h07'57"
Total time ?

Second rider: Accum. time: 52h27'21"
Next stage: 4h02'45"

To calculate: New total accumulated time
New difference to leader
To present: New ranking list

in other words: How to simply add (and subtract) hours, minutes and seconds without taking into account any dates.

Thank you for any help.