Actually it's less paperwork. I fly for scheduled airline and our flightplans are stored, wx brief is prepared by dispatch when we check in at ops (1 hour befor separture), 99.99% of the time W&B is done by the airport load office and oil check is performed by line maintenance. Basically, there's lot more of checking other people's paperwork than doing your own. We show up on airplane half-an-hour before departure, and if everything is running fine, the airplane is ready 10 mins later. Turnaround can be brought down to 15 mins but that requires heavy cooperation from airport services.
That's for ATR, I guess it's a bit more time on A320 if only for the sake of longer walk during walkaround. Given luck, I'll be able to give you precise answer in couple of months.