Hi
I am only going from MVMCP last year. We booked our tickets about 2 weeks before we went last year for a Thursday evening and we were fine. On the night people were buying tickets from the booths and as far as I could see nobody was being turned away. Fridays do sell out first though.
I booked my tickets though for MNSSHP as soon as they were released this year as we could only really do the Friday but also as I knew that they were paid for. I would keep my eye on the Disney web site though as they tend to show when the dates are sold out. If they do look like they are selling out fast you can always call up and book them, otherwise wait until you get out there.
Good luck.