Dd2's school had a revision skills session from an external company, and they also did one for parents but I couldn't go, but they emailed us a summary afterwards.
I've copied a bit that seems relevant:
"It is better to work for less time in a concentrated way than to work for longer with less focus.
The optimum time a student should spend revising without a break is 25 minutes. We recommend that students complete three twenty five minute sessions in the morning with a five minute break between each session. This should be followed by up to three further one and a half hour blocks (with five or ten minute breaks every twenty five minutes) in either the afternoon or evening. Students also need to plan “days off” and “treats” within their timetables.
The first 60 seconds should be to work out what they are going to achieve in their session and the final three minutes of each session should be spent simply re-reading the notes they have just made."
Dd2 said that for her 25 minutes is too short, she's just getting started, so she tends to do up to 40 minutes, but the plan is similar - two or three shorter sessions with little breaks, then a longer break, then repeat. She's also making sure to get outside each day.
Dd1 of course knows better, and is sleeping most of the day, spending the rest on the internet/netflix, going to the pub in the evening, and finally sitting up half the night producing beautiful flashcards! (I may exaggerate!)