A typical Ryanair departure for us at EMA is to have two staff on check-in with both of us proceding to the departure gate after checkin closure 40 minutes before STD. As soon as arriving at the assigned gate, call for screens to be updated to show boarding gate, then put out call even if the aircraft isn't on stand yet. That way, once we do get the go ahead to board, most people are aware of & have migrated towards the assigned gate, with PRMs & 1-90 already waiting to board. I think EMA is one of the only airports where cabin-crew don't assist with the boarding process, rather we send down 2 CSAs.
To me, the 25-minute turnaround is an essential part of the no-frills airline model, and it has been safely & professionally done for decades in the states, and just over a decade here in Europe. I don't think 20 minutes is a good idea, but 25-30 is optimal both for us & the airline, if it is handled correctly ie proper staff utilisation, training, incentives & numbers. It also helps if the airport is equipped to handle 25 minute turns.
By chance, could anyone tell me why at AGP & ALC some low-cost airlines who usually schedule 25-minute turns schedule 40 minutes at these airports? FR (B738s) keeps to 25 mins at AGP & TOM (B735s) 30 minutes so surely it can be done?