I do Ocr so it might be a different but I find that it takes rouphly:
8 hours for C1
10 hours for C2
12 hours for C3
10 hours for D1
10 hours for d2
12 hours for S1
18 hours to do fp1
(Only modules I've done so far)
To consistently get an A (~85ums)
To reliably get an A* /full ums (~95-100ums), I'd expect to spend around an equal amount of time practicing and doing past papers.
The content isn't all too difficult for the modules I've done, most of the time spent is on doing paper and questions to ensure you have a wide applications of the skills.
I presume that for A2 modules ESP the harder further pure and mechanics, it might take 40+ hours.