You can take The PM PrepCast final exam 2 weeks after you purchased the course. We make you wait for 2 weeks because if you study often and much then 2 weeks is about the shortest time you can take to watch all lessons.
Once you have taken the final exam, you get the 35 contact hour certificate and then you can apply for the PMP exam.
However... many of our students are experience project managers who already have more than 35 contact hours and they use The PM PrepCast to study the concepts necessary to take the exam. So these students can apply for the PMP Exam immediately.
I think what I say is: "you should apply for and schedule your PMP exam as soon as you fulfill all eligibility requirements". And you can imagine that with over 8,000 students there are 8,000 stories as to when they all meet these criteria.