I generally say about an 60 minutes for AK, EPCOT and HS with MK perhaps 90 minutes if really, really unlucky. This is longer than some here are saying, but that is my experience.
For example, 30 minutes to drive to the park entrance. 10 minutes to get to your parking spot and unload. 10 minutes to wait for a trolley or walk. 5 minutes on trolley. 5 minutes to walk to the turnstiles. Now it can certainly be less, but 60 minutes is a good place to start. You won't be disappointed if you make it in 40 minutes.
At MK, you have the extra 20 minutes or so of getting from the TTC to MK. If unlucky you can arrive just as the ferry or monorail are pulling away and have to wait longer, so suddenly it feels like it is taking forever...
Other factors include how many kids, strollers and stuff you have to lug around. That stuff will slow you down some.
Distances are pretty vast at DisneyWorld. There can be traffic and crowds. Give yourself enough time.