Yes. You don't need to study that HARD, but rather study smarter so that you are spending time more efficiently. Plan out your revision carefully, and also ensure you're taking breaks and do LOTS of past papers.
To be honest, I revised like from 2-7 days for 4 AS/A2 modules for maths and got 90+ UMS in nearly all of them. This is maths, but my point is, you should study smart not long. I'm an advocate of focusing 100% in class and doing the minimum amount of work that will get me understanding the topic at hand.
This means for me - not studying 5 hours after school every day, however if you NEED to study that long in order to understand the topic fully, feel free to. Honestly, I'm going to work a lot harder this year for Y13, but I know realistically that if I want an A in a specific subject, it won't be too difficult - it's the A*'s that you need in a SPECIFIC subject that you really have to work hard on.
Edit: Have you not factored in burnout? The law of diminishing returns (i.e. productivity in this case) applies to studying also. Break it into small chunks and you will gain more productivity for a lower amount of time. This about it like this graph:
don't study hard.. study smart.. look at your weaknesses. in french for example, is it vocab, grammar essay writing?
Hey buddy that's my saying!.. I'm glad you're promoting it
With 5 hours revision most days for 5 months I wouldn't expect BBC, I'd expect AAA. You need to understand how you enjoy learning, do you like visualising (linking stuff with pictures)? Do you feel that simplifying something makes it easier to remember the expanded information? Is there anything you struggle with in particular? Have you created an effective timetable?...