Are you going at a slow time? If so, you will probably be seated right away (we were for all our ADRs on our trip last week, very low crowd levels). But even so, by the time you sit down, eat, see all the characters, and pay you are most likely looking at 45-60 minutes in the restaurant. Best case scenario for transport to the MK, you walk out and a monorail pulls up for you right away. Worst case, you wait 15 minutes for the next one.
I would guess that you're looking at walking into the MK at the earliest at 9:00 and more likely sometime between 9 and 9:30. But as long as you do Dumbo first, you're probably OK. If you get there after 9:15, you won't walk on, but you shouldn't have a 40 minutes wait either.
Getting there earlier may help. I would aim to be there at 7:45.
Beth, mom to older DD (8/01) and younger DD (10/06) and always missing Leah (4/22 - 5/1/05)