well i did health and social care in a year i had 4 as lessons and 4 A level lessons a week (2 1 hour and 2 1 hour 20) and then we were recommended to do at least the same again at home
so rough guesstimate..
lets say 18 hours a week... for 9 months.. so if recommended minimum hours - 648 hours... 27 days ... start now dont stop dont eat drink or sleep and you could do it in month ... theoretically...
I reckon if you dedicated 6 hours to the A level a day (excluding weekends) you could probably study the whole thing in about 2 months. Having said that. I'd say probably longer for sciences (due to the fact that theres so much to be learnt).
Depends on the grade you're looking for, how fast you can read and write and how good your short term memory is. If you're good at all of those you could probably get a C to an A in 30-40 hours of studying and doing past papers plus some serious cramming before the exam.