The actual monorail ride time to the TTC is almost exactly 6 minutes. That means, if you miss a train at Epcot the wait time will be about 6 minutes, plus 4-6 minutes in station wait time. So 10-12 minutes to get to the TTC.
At the TTC you transfer to the Express monorail. About 2-3 minutes to crossover. If the train is there you'll have about a 2-4 minute in station wait then 5 minutes to the MK station. If it's not there then add ten minutes.
So the longest travel time is about 30 minutes. That's monorail travel time from platform to platform. As PP said though, plan on at least 45-60 minutes Epcot gate to MK gate.