My understsanding is the same as Chuck's - 90 days from your check in date, you may call and make PS/ADR arrangements for your entire stay (as long as the stay isn't more than 10 days).
Diane - According to other posts, Disney only opens a percentage of the available PS/ADR times for the 90+10 people. If you call at the 90 day mark, you shuld still be able to get what you want. Good luck to you!
Best wishes -