Hi, Sharon!
The two Walt Disney World theme parks that are closest to each other are
Epcot and
Disney's Hollywood Studios. These are the only two parks that you can actually walk between (about a 2 mile/30 minute walk). You can also hop between these two parks via boat service, bus, or your own car. Once on the road, your drive time between parks is about 15 minutes.
On the flip side, the two parks with the most distance between them is Magic Kingdom and Disney's Animal Kingdom with a distance of about 11 miles. The bus ride between these two parks is about 25 minutes.
Traveling between any two parks will take anywhere between 15-30 minutes, but always allow time for waiting for
buses/trains/monorails/boats as well as any stops they might make along the way. If traveling between parks for a reservation, I usually allow up to 90 minutes to include wait time, travel time, security, and usually getting distracted by some fun gift shop!
Wishing you happy travels around Walt Disney World property!
Cathy