Even with our toddler we spent 4 half days at Epcot when we went in December. We only had 5 days to spend at WDW so we park-hopped a lot to get everything done. We spent the least amount of time at MGM, 3/4 of a day, but still did everything we wanted to do there, including all of the 'thrill' rides. I would probably pencil in a full day at Epcot then another evening for dinner and poking around WS some more.
But like everyone has said, if you're not interested in the countries at the WS or some of the displays and slower rides in FW, you can probably blow through MS, TT, SE, and Maelstrom in half a day max.