In the movie "Back to the Future," what speed does Doc Brown's DeLorean need to reach in order to travel through time?

In the movie "Back to the Future," Doc Brown states that the DeLorean time machine needs to reach a speed of 88 miles per hour (mph) in order to travel through time. The specific reason behind this speed is not explicitly explained in the movie. However, it is widely believed that the number 88 mph was chosen by the filmmakers because it is a visually appealing and memorable number that adds to the overall excitement and mystique of time travel in the story.