Time overlap

Hello,

I have some difficulties calculating the right time from 2 periods. I`m looking for the total sum where vessel 1 and 2 are used.
The problem is:
I have on a row 2 time periods (total 4 colums eg: start stop, start, stop). I managed to calculate over here wat the overlapping time is and the not overlapping time. However, the next row also can have a time period overlapping with the first row.
It also can be that the next row don`t overlap any time or misses information.

Can someone help me do this trick?

See also attached file