Hmmm...define "decently."
I'd say:
1 day for Animal Kingdom
1 day for the Studios
2+ for EPCOT
1-2 for Magic Kingdom
So that's about a week. And you could fit DTD and a little resort-hopping in there.
You'd have to add more days if you wanted to go to the water parks, miniature golf, regular golf, etc. And even more if you wanted to venture off-property (Universal, Sea World, Kennedy Space Center, beaches, etc.).
I wouldn't recommend you schedule a trip for fewer than 5 days. Stay more than a week (especially in the heat), and you'd want to move at a leisurely pace--that is, if you wanted to move at all.
