I am a doctor, have done a lot of exams including specialist exams and am good at exams😀.
I found that at medical school level and specialist exam level the people who did well were efficient at study, generally organised, exercised and weren’t burnt out, so could step it up when they had to. The people who slaves away for hours every night for months on end often weren’t as good at exams.
There’s no guarantee of success with quantity and shorter, but more mentally challenging study, is much more useful.
Some children can spend hours rewriting study notes, highlighting things, re writing the highlighted passages, filling books with study notes. A lot of it is a waste of time.
It’s much more effective to focus on what will be examined, maybe make up exam questions to be answered with clear content, lots of past questions and no endless writing of lists but actual learning of lists. Then practising using that information in the same way it’ll be asked in the exam.
Effective study is harder but doesn’t necessarily take as long.