How many subjects do people recommend studying per night?

I'm doing 10 GCSEs:
Maths, English Lit, English Lang, French, Biology, Chemistry, Physics, History, P.E and R.E

I'd say start with the ones your not as confident with and spend the night on that one subject and do that for any other ones you might not be as confident with. Then with the subjects you are more confident with spend a night just going over the topics you need. Don't worry if you feel like you don't have enough time because your school should collapse the timetable to give you more independent revision time with teachers there if you need them.

But remember don't overwork yourself because it will be harder to retain the information. I'd say stop revision at 6/7 every night, to give yourself some free time before you go to bed to watch your favourite tv shows/films like Thor: The dark world or Captain America: The winter soldier to calm your brain down before you try and sleep. It works promise, because this is what I did for my GCSE'S and I came out quite well :-)