We hadn't heard about ADR's before planning our WDW visit, so every time we've been to DLRP we just turned up on the day or on the last visit pre booked the day before as we really wanted to eat at the Blue Lagoon again, we always managed to get everything we wanted except for Walt's which was a last minute decision at 12:30 in Aug so not surprised we couldn't get that. We have visited in Aug, Sep & Oct.
In my experience as long as you are flexible with your times you should get most of the places you want.