We had an ADR for 5:10 p.m. on Saturday (9/10). Got there and there were at least 20 ppl waiting to check in in front of us... BUT, we got a pager and were beeped within 5 minutes. We were done within an hour (5 adults plus one "infant" who ate more than I did!!).
I think you can do it, but only if you catch the monorail back at the right time AND eat quickly. If you take the walking path, though, it's a goot 10 minute walk. You also probably will not have a good seat upon arrival.