I did **** all over xmas when I was doing A-Levels. All of you who are doing 5/6 hours of revision a day are either-
1) Incredibly thick
2) Incredibly boring
3) Doing the wrong subjects
or
4) All of the above.
And hour a day, per subject, with the occasional work free days where you go outside and play with the snow or with yourself or something should be more than enough. An hour of good study where you actually critically appraise and question what you learn will do more for you in the long term as opposed to stare at a page for hours on end making a ****-load of notes that you'll never ever ever need.