I had mocks in November and February and so I revised a lot for those. I then started to revise for actual GCSEs at the start of April, which I think was too late as I was quite stressed.
I got (in 2022)
English Language 6
English Literature 6
Computer Science 8
Food Tech 9
Combined Science 99
History 8
Maths 8
Spanish 8
My advice
Do practice questions for revision - especially maths and science
Flashcards for languages
Essay plans for history
Craig and Dave (I think) for computing. They do a free YouTube channel and then paid practice questions.
Use your mocks as revision, so revise seriously for them.
I would say start to revise at the start of March, so you don't have to rush and overdo it right before. There will always be time to revise, depends on the effort you put in.
I depends on the subject, but I would say 2 hours a day for a month ish and you should improve. But the revision has to be active and useful.