Check airman
Main consideration for APU bleed is it sucks in engine fumes. APU starting takes 40 seconds and if you start it after engine shutdown till 5% N1 it has to be atleast close to one minute delay and it will recycle packs. So as Uplinked says it could bring in another aspect. So it's an issue which needs to be airline policy rather an individual technique. In Airbus best thing is to refer it to Airbus which will consider these aspects in their answer. Personally I would not cut it so fine. APU has nothing to do with 3mts.