I only did an hour a week of each subject but started revising at the beginning of year 11 so if you feel you're behind with revision you could maybe do 2 hours. You shouldn't be revising more than two hours on a school day or you'll get burned out. The only things I did for revision were making mind maps and testing myself on them and doing practice questions. For French you should get duolingo and do things such as watching French tv, try to watch cartoons in French without subtitles then it won't even feel like you're revising when you are