You can back into the time pretty easily.
Worst case scenario, you have a 10-15 minute wait for both monorails. Maximum: 30 minutes
Ride to TTC, unload and walk to Epcot platform is about five minutes in the morning.
Ride from TTC to Epcot: about 10 minutes
So worst case would be about 45 minutes, but you could get lucky and not have to wait for the monorails, which would reduce the time by about half. It also depends on whether it's busy and you have to wait for a second monorail at either stop - doesn't happen often, but more likely at TTC than at the resort. If being there at rope drop is extremely important, I would probably allow an hour, just in case there's a hiccup somewhere along the line.