Disneyland Opened in 1955 so it took 1 year. Construction began on July 18, 1954 and opened exactly one year later. Construction of Walt Disney World began in 1968, and it officially opened in October 1971. So, it took approx. 3 years to build Walt Disney World. But keep in mind construction is ongoing and Disney world is most likely going to expand.
One year for Disneyland. Ten years later, Disney World was built. After the start of construction, Disney world opened after three years. But they are always expanding, and Walt Disney said that as long as there was imagination left in the world, it would never be finished. No, I didn't have to look any of this up.