Most Airlines prefer you get the Flaps up before you engage the A/P.
I have never heard this one before. What is the reason for this?
There are some airports we operate to that I try and get the AP in as soon as possible after takeoff due to the high workload associated with low altitude level offs and ATC instructions and frequency changes, so it just overloads the PM if AP is not engaged at at 400'.
Of course this does not always apply and I quite often hand fly a bit longer, but we do not have any specific company policy except the Boeing limitation of 400'.