It depends on your skills , experience. As I purchased the second part at the beginning of April I even didn't know about the deadline of August (now postponed to October). But as I read it, I firstly thought 4 months are not enough even with my experience of nearly 10 years, as I really planned to spend only some hours each Saturday. So I looked for many advises. But then I told my self : simply start. So I spent 2-3 hours daily after work in the first 2 weeks (I also have family and son) and after 2.5 weeks I have done nearly everything. Then I spent another 1.5 weeks correcting something and writing down some thoughts. After 4 weeks I didn't have something to write and took part 3 on May 6. I think I spent between 45 and 55 hours for part 2 and only few hours for part 3, simply reading this forum preparing myself for the questions
Of course I tried to find a compromize between good assignment and chance to resubmit it till August. You don't have this chance, because it now takes more than 2 month to grade. But if you'll work daily on assignment you'll do it. It's worth doing it, as you won't need any expensive preparation course for upgrades and I hope, that
J2EE 6 Certification will be offered soon. I don't think there will be many programmers wanting to be certified paying so much money for the preparation course, so this certification will be even more valuable for sure
Hope I could help