I mean I assume you are talking about the exams that happen in late May/early June this year not January or whatever; if so then start revising now! Yes, you probably could do just fine on a months of solid revision (I mean I don't know what you are aiming for, or can physically achieve) but the more time you have the better because then it's more likely to stay in your brain. So start revising now and you won't have too much trouble hopefully!
Good luck with your exams - I'm in the same boat and very nervous!x
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