Hi,
I did GCSEs last year (and apart from PE got mostly 8-9 with a few 7s and As, so all this comes from experience.
Having just done mocks you want to b giving yourself at least a short rest...for the next week or two I would suggest that you just did homework and not too much more, if anything. After that it should be the holidays, so I would start by making a list of all the hints that you felt most uncertain about in mocks and doing maybe 1-3 hours a day with a rest day at some point in the week, focusing on those things. And of course have the Christmas period off! Mainly this holiday, though, you should be resting and recouperating ready for next term, Also, I tend to count the hours I do a week rather than a day so that if one day changes somehow I can reconfigure my week a bit and not feel bad about doing less on a particular day.
The number of subjects a day depends on what works best for you-all I work best having subject specific days where I really go to town on science or maths or French or English and nothing else, but that's for you to decide.