The wait for the monorail once you reach the Epcot platform should be 20 minutes or less. I frequently see the Epcot monorail running on a 15 minute cycle when I'm waiting to take pictures of it in Epcot. It will be a 5-10 minute trip to the TTC. Once at the TTC, you can either switch to the resorts monorail with a second wait of up to 20 minutes followed by a 3 minute trip or take the short walk to the Polynesian. So a 3 pm departure from Epcot should work okay. If you're running late, it may actually be quicker to walk from the TTC than to wait for the monorail.