On the A320, 20-25 minutes will actually give you enough time to prepare the aircraft and depart on time, granting that everything is in place (i.e. no technical defects, no expected delay from ATC). Remember that as per typical airline SOPs, you don't have to do everything by yourself, and by that I mean PF and PNF task sharing (i.e. PF prepares the FMGS while PNF performs the walkaround).
It's basically the same thing for the A320 as it is for the ATR. There is not much paperwork in the cockpit because practically everything has already been sorted out the moment you check in at dispatch (WX briefing, Fuel Planning, NOTAMS, etc). In my experience, sometimes it takes even longer to get on to the aircraft than preparing the aircraft itself because of the time you spend travelling from dispatch to the terminal, going through security checks and all that.
That's why in my present outfit, flight crew report to the dispatch 1 hr before scheduled departure and cabin crew 1 hr 30 mins. We normally send the cabin crew ahead to the aircraft so that by the time we arrive there the aircraft is ready for boarding.
So that's it. Just be systematic like i said and you will save yourself a lot of unncessary worries.
Happy New Year and wishing you all an on-time departure all the time!
