When you bring up numbers like 90+ you are talking about percentiles (i.e. how many people you beat) so this is actually all relative on how every performs in the UMAT, non predictable unfortunately. Your actual UMAT score should be triple digits (eg. 155,175,189) which is then used to determine your percentile, ACER also do not release any data in terms of raw marks (/134)=what UMAT score so it's all guesswork.
Tips:
-Probably do a preparation course (medentry is best) for S3, it's the only section that can be tutored and from my own experience it does work.
-Practice papers help with getting used to the 3hr concentration time (1 a week is pretty standard)
-Make sure you really want Med/Dent etc before you spend the fee on ACER and courses
Never too late to start studying ofc