Remember with the PPL exams, some can be done with minimal work. Ones like Navigation, Human performance & communications can be done in a few hours work, simply because you have already covered alot of the questions in the PPL flying. Ones such as LAW and MET take alot longer through the sheer amount of stuff to read.
On the subject of the ATPL's they are very similar, but go into so much more detail. I have so far done about 40hours a week for the last 5 weeks and still have another 6 weeks before my brush up course and then about another 80-100 hours at the brush up course. So it will be near 400-500 hours of work for 7 exams!
I think I said it earlier but if you plan on doing the ATPL's then make the PPL exams count , the more you learn at PPL the easier it is to understand the ATPL's, it all counts.