How much revision should I be doing for A level 2 year?

I don't know how much to do or how much to balance my time between subjects. I'm a second year. So how much time should I spend on each subject now and over Christmas. I'm predicted ACC but I definitely want higher and I have changed my revision strategy recently so my revision is more productive. I don't have specific grades in mind I just want to do my best.

My sixth form says that for every lesson you have, you should be doing an hour outside of lessons. This does include homework and stuff though I think. I'm not sure how much truth there is but it is the only thing I've been told.