Since a lot of Ryanair flights are relatively short hops, that would at least cut down on refueling time, if not just fuel every couple of legs if the economics work out.

Cleaning is definitely sometimes abbreviated, I've been at the stand for a Ryanair flight in Leeds, seen the previous passengers get off, then they boarded us five minutes later (the inbound flight was late, so maybe not standard practice)

Cleaning happens between deboarding and boarding, not in parallel.

Normally there are no particular checks that can't be done from the cockpit at turnaround.

Refuelling takes less time than that typically.