While some of its staff were in 1955, young Biff Tannen stole one of the new DeLorean time machines and began skipping wildly across decades. Doc sent a crew in to follow Biff and bump him back to the present.
A demonstration model was built by Doc to demonstrate to the time travel volunteers at the Institute exactly how time travel worked.
Behind the scenes
The events that led to Doc selling the Institute to Krusty the Clown in 2006 were developed as part of The Simpsons universe crossover to explain the history of the building. However, this information is non-canon.