Actually, the 03 GM transmissions used by BMW have "unfavorable tolerances of C1 clutch housing causing internal trans pressure leak after extended parking". So, the fluid drains out after sitting, and when you put it in driver, it takes a while to build pressure and engage.
BMW is replacing these transmissions. Make an appointment with the dealer, so you can get on the list for a new transmission....
we are doing a LOT of them, and new trannys may be slow in coming.
There is a service bulletin for this. The symptoms are a delay in transmission engagement to drive, on cold start.
E46 with GM5 9/02-12/03 or 3/03-12/03
depending on the model car.