Is one day enough?

Is one day enough to do EPCOT and MK ...
I would advise 2 days minimum especially if your a major potterite.

I would say at least 7 years..

I was able to do mostly everything at Universal in a couple days. That was with everything being almost completely walk on. It also depends if you want to do both parks or just one.

You can hit the highlights at both Universal parks in just one day, especially if crowds are low. If you want to do EVERYTHING, though, you'll want two days.

Edited to add: you can easily do Diagon Alley, the Hogwarts Express, and Hogsmeade/Hogwarts in one day, if that's all that's really important to you, and you should even have time for a few other attractions.

You can do it in a day, we did last November. Crowds were so low we felt like the only people in the park at times and the ony thing we had to queue for was the Gringotts ride, and that was because it kept breaking down otherwise that would have been pretty smooth sailing too.

We've been to Universal before so we knew we wanted to hit our favourite rides and check out whatever was new since the last time we had been (around 2 years previously). I don't remember watching many, if any, shows, apart from the Hogwarts Choir, and we did sit down a while for lunch in the Hogs Head. Nothing felt rushed, everyone got to do what they wanted to do and we had a brilliant day bouncing between the two parks.

We spent most of our time exploring all of the Harry potter stuff but still went and did things like The Hulk, Men in Black, Terminator, The Mummy, etc, like I said, we hardly queued for anything. We got to the park at opening and left about an hour before closing time.

I agree.... especially with Diagon Alley being open. We spent a lot of time with HP, but we also had a blast with the other attractions and did most of the rides several times. Don't get me wrong.... we are all about Disney, but there are some rides at UO that my family loves that are a different experience than Disney. So when we travel as a whole family, not just DH and I, we make time to visit the "dark side".

It will depend on what rides you definitely have to go on outside the Potter lands.

You'll need a ticket that covers both Island of Adventure and Studios in order to ride the train from Hogswart and get off at King's Cross otherwise you'll be stopped from getting off.

Plan it right and you can whip through the parks in a day but it will be long day. I managed it with my parents, but they didn't follow me onto every ride, so I was able to get through on the single rider line when I was on my own.

If you can, though, 2 days will make it easier and will give you ample time to enjoy the dark side...