Ukcat & bmat

Focus on your first year exams. It only takes a month to prep for the UKCAT and BMAT. Some even only do a couple of days of prep. It is aptitude testing after all. If you want to find out each test is like, structured or scored, just visit their websites. It has everything you need.
https://www.ukcat.ac.uk/
http://www.admissionstesting.org/for-test-takers/bmat/

There are no other admissions tests YOU need to be concerned with since you are applying for undergrad entry.

You can book your UKCAT anytime from June-September (check the website ^ for precise dates).

The BMAT everyone sits on the same day like a normal exam either in September or in November. Not many do the September one since it's straight after your UKCAT and there aren't many centres which allow you to do the Sept BMAT. Also be aware that unis like Oxford DO NOT accept the September BMAT. It must be sat in November. So I recommend sitting the November BMAT as you'll avoid the hassle and have plenty of time to prep.

As said before, you do not need more than a month to prepare for the tests.

I am aware the UKAT and BMAT exams are required for medicine, but I have very limited knowledge about the two. I want to start studying for them but I want to focus on my AS exams to ensure I achieve the best grades possible. I have a few questions regarding this. Firstly, are there any other admission exams for medicine? Additionally, when are the exams for 2018 and hence when would be a good time to start studying for them?

Thanks.