The shorter formula I got does work as well, except for column D where
0:00 start and 01:00 end are stored.

AND I figured this is still a bit too long (255 characters does not "copy-sheet" and needs "copy cells")

Thx
LEO

+IF(+IF($AB12AT$9;0;MAXA(AT$8;$AB12))=0;+AT$9-MAXA(+IF($AB12AT$9;0;MAXA(AT$8;$AB12));IF($AC12<A T$8;0;MINA($AC12;AT$9)));AT$9-IF($AB12AT$9;0;MAXA(AT$8;$AB12)))-(AT$9-MAXA(+IF($AB12AT$9;0;MAXA(AT$8;$AB12));IF($AC12<A T$8;0;MINA($AC12;AT$9))))