I would plan on being out at the bus stops no less than 45 mins prior to park opening. There will be a lot of other people doing the same thing. While it might be just a 10 min ride, you could just miss a bus and have to wait for another one.
If you are driving.....I would figure on about 15 mins to MK, well the TTC. Add another 15-20 mins once you get into the lot. To Epcot, figure on 10 mins, same for DHS. AK will be 15+. But again, if you leave it until too close to opening, it will take you longer because you have so much company.