Do you think I will be able to acheive an A* and A overall this time?

I'm resitting two of my a-levels to try and get into a good RG uni: My current grades are BCC but I want A*AB so I'm retaking Biology and Chemistry.

My practical grades in both subjects were really bad (D-U) but my other module grades for Biology were BBA* and E (due to family circumstances) and I Chemistry CCCB. Do you think I could do it?

With the right kind and amount of work, yes. Obviously, nobody here can make certain predictions based on one TSR post, but the 'work smart, work hard' formula seems to work for most people.

That is good, assuming I start revising now how many hours a week should I be aiming for if I want to resit only one unit I the Biology and all units in the Chemistry?

The optimal number of hours -- if there is indeed such a thing -- is quite variable depending on the person. If you're one of those people I knew at school who could virtually inhale information from a textbook and then sneeze it onto an exam paper, then probably not very many hours.

However, if you struggle with recall, then you'll need to experiment with things that help you retain information (e.g. mind maps, tables, writing and rewriting notes etc.) and how much time you need to put in would depend on how long it takes you to do those things enough times for you to remember information.

I'm probably not the best person to answer this question because I never really developed any real revision technique. My whole approach throughout my school years was to do very, very little during the year and then learn the whole course at home just before the exams. If you opt for that, you'd be looking at 16 - 18 hour days purely because there aren't that many days left before the exams for you to get all the necessary information and complete some past papers.

In summary: Don't aim for a certain number of hours. Find a way of learning that suits you and learn at your own pace. It's quite early in the year so you can afford to do a little every day and stay within your comfort zone. Just do whatever you're comfortable with at the moment -- you've got plenty of time to iron out problems between now and May/June. If anything, it might be detrimental to start too early because you might forget things if you cover them too early and then don't revisit them often enough!

I can't really afford to do the 16-18 hour thing because I work to support myself on top if this aswell so I'll probably just stick to an hour or two until early February then bump it up a bit.

That sounds healthy. Yeah, the 16 - 18 hour thing is really only necessary if you've left learning the whole course to the last week or two before exams -- there's just not enough time to be doing an hour a day at that point. Starting now and doing a little every day sounds a lot nicer to be honest.