I've calculated the precise distance, taking into account the acceleration speed and wind resistance retroactive from the moment the lightning strikes, which will be in exactly 7 minutes and 22 seconds.
16 seconds sound clip from the Back to the Future movie soundboard.
You can hear this line at 01:32:17 in the Blu-ray version of the movie.
Quote context
[...]
- All right! Let's set your destination time.
- This is the exact time you left. Let's send you back at exactly the same time.
- It'll be like you never left.
- Now, I painted a white line on the street way over there. That's where you'll start from.
- When this alarm goes off, you hit the gas. Right.
- Well, I guess that's everything.
[...]