Night holiday charter flights are the NORM in the summer lol not the exception!
Just toddle down to Palma or Rhodes and see for yourself on a hot summers night
Airlines like TUI may squeeze 4 rotations in to a 24 hour period - We did at Monarch back in the day, although 3 was the norm.
Court Line certainly did 4, but the routes were shorter then, like the nearer Med rather than today's medium hauls like Cyprus and Egypt,
As mentioned there has to be downtime during the week for Engineering checks but generally these were done at night or early hours of the morning before the first flight out.
IT charter aircraft are busy busy busy with little or no ''play catch up'' time available especially within smaller airlines who may have no way to bring in a spare -
We saw TUI this summer doing a pretty good job to keep their flying going with a lot of ACMI work, and swapping their own fleet around all over the place.
EZY and FR may well do 6 -8 cycles a day on shorter routes with an aircraft, and as discussed there are few late night returns for their fleet, although EZY does have more night flights.
Jet2 ? - not so sure of their schedules.
All of these 3 LCC airlines do have spare aircraft or can shift them around to cover AOG situations, but maybe not everyday during the summer peaks or on 'bad days'
Spare aircraft lying around were not a luxury with any of the holiday airlines I worked with and 12 hour+ delays were common, either due to ATC or Tech issues.
At BMA our DC-9's all returned to their bases at night (MME LPL GLA EDI EMA and BFS) after bringing in the last flight from LHR, having done around 5 round trips that day.
We did try during a few summers to do some night IT charters when the aircraft got back - off down to Rimini Pisa Ibiza Palma Alicante (short flights) BUT if there was fog or bad wx on the inbound back in, or a hold up say down in Palma, that would mean a delay to the first early morning departure down to London which we could not tolerate the risks to upset the businessmen.
So we didn't do that many. I guess that model applies today to FR and EZY too.