I would say leave no later than 6:00 and you should be fine. The ride is (they say on the monorail announcement) about 10 minutes but it seems to go faster than that. By the time you get off the monorail, go through security and then turnstiles and get to your ADR (not sure where you're eating), you should make it. I wouldn't hesitate to even leave a little earlier than 6 if you can manage to. I say this because you can "leave the park" at one time and by the time a monorail comes (there could be one waiting but don't count on that), you could be talking another 10-15 min. wait. Also, if your ADR is on the other side of Main Street, cut through the stores so you're not swimming upstream, lol. Just say to yourself "i'll buy this stuff later", lol.