In column "J" I enter certain codes (2 digit numbers), in column "M" I
enter date+time and in column "O" I enter a duration in HH:MM.
I need a formula doing the following:
Whenever there is code 50 in column "J" and the date in column "M" (same
row) is greater than the date in $B$3, then the time in column "O" has
to be added. There can be more than one rows with these conditions
though, I need the summary of all times entered in column "O". Hope it
(I) make sense.

Is that possible? I think it could work with SUMIF(AND(..... or maybe
even better with a SUMPRODUCT formula.

Regards,
Norbert