If you feel like you're not revising 'enough' try to wake up earlier - it helped me gain some extra time in the morning so that I didn't have that many things to do at the end of the day! When I was revising, I think I revised around 8 hours per day being homeschooled but if I did have classes, I'd try to get in min. 5 hours of post-school revision time but you need to see how much time you have left before the exams, and decide for yourself how much you should and most importantly, can revise - it's vital that you don't overwork yourself.
As a general rule of thumb, if you want to put in more hours, you need to make sure you're revising efficiently/effectively and that you're not doing it for the sake of 'getting more hours in' because it can be counter-productive. As you know, revising for 6 hours with great focus and understanding is much better than revising 10 hours with sporadic periods of immense focus only.
Lastly, remember to rest, drink water and good luck!