the advanced testing at PSA is based on hours, don't quote me but 20 hrs rings a bell. IIRC the only difference is that the advanced guys do more elaborate aerobatics, ie barrel roll etc. and have less time allocated to circuits etc.
PSA is difficult but if you have a passion for flying and they can see sufficient progression in your skills, they will score you well. i thought the OSB was pretty full on, but if you show confidence and a level head in what is meant to be a stressful situation, then you should be fine. mental maths is part of it as LJR pointed out but it probably amounts to 2 or 3 questions.
know your squadrons and aircraft specs (top speed, range, payload, role etc.) as they do probe to get an idea of your depth of knowledge.
thats about all i can remember, hope it helps.