I made my TTC reservations yesterday for our trip in October. I know how you can feel that if you make them too far in advance, they might forget you? TTC is very efficient and gave us great service last year. Go ahead and make them now, and if you'll feel better, call them and confirm a couple of days before you leave.
Makes absolutely no difference at all. Months in advance will get you the same service as calling the day before arrival. And you pay the prevailing rate at the time of the pickup anyway.