I can't relate to this because my exam timetable is actually pretty generous, however I feel your pain. Try to be glad that your exams finish quickly and you can relax - mine don't finish until the second last day of the exam period! Also, try to find comfort in knowing that there are a lot of other people in your situation

Unfortunately, your timetable is something you can't change in the slightest. And as a result, there's not much point in stressing out about it. I think there's a quote that goes something like "if you can't change it, change the way you think about it".
The thing is, you do all of your exam revision in the weeks/months leading up to the exam period (minus maybe reading over your notes a few times or w/e). Your revision isn't something that you do in the few days leading up to your exams. So, having your exams bunched together doesn't really mean you lose revision time. It just means that you need to be able to sustain a high level of concentration and effort for a few days.
As a result, you need to learn coping mechanisms for dealing with high loads of work/stress. Whether that be meditation, exercise, colouring in, or whatever, so that you can keep your mind clear during the exam period. Do plenty of practice exams, etc. not only to test your knowledge of content, but to also make sure that you're used to sitting down and concentrating for a sustained period of time.
It's easier said than done (and I'm blessed in that I find this easy to do), but once you finish an exam, move on from it. There's no point in worrying, because you can't change your answers. And if something goes wrong, use that as motivation to ace the next exam, and show the assessors all the knowledge you have about that subject

And remember, year 12 isn't the be all and end all (such a cliche but it's true).
Hope this has helped a bit