hi, Stefan !

... two columns with date + time like this
Startdate Enddate
11/08/2004 19:00 11/08/2004 22:17
11/08/2004 19:30 11/08/2004 21:24
11/08/2004 22:30 11/08/2004 23:50
11/09/2004 00:00 11/09/2004 00:31
11/09/2004 00:30 11/09/2004 04:31
11/09/2004 02:00 11/09/2004 03:20
11/09/2004 15:00 11/09/2004 15:12
... sum up the difference ... between each row ... will get the total ... minutes but I'm looking ... effective time.
Some ... records are overlapping ... record 2 fits inside the frame of the first record [...]

might this could work?
assuming record entries in range A2:B[n]
[C2] -first record- 'by default'... formula: =b2-a2
[C3] -from second record-... formula is: =(b3max($b$2:b2))*(b3-a3)
drag/copy/down, and you can now sum 'C' column -number format [h]:mm<-

hth,
hector.