It says here that a bolt of lightning is going to strike the clock tower at precisely 10:04 p.m. next Saturday night!
9 seconds sound clip from the Back to the Future movie soundboard.
You can hear this line at 00:54:28 in the Blu-ray version of the movie.
Quote context
[...]
- Unfortunately, you never know when or where it's ever going to strike.
- This is it! This is the answer.
- If we could somehow harness this lightning, channel it into the flux capacitor, it just might work.
- Next Saturday night, we're sending you back to the future!
- Okay, all right. Saturday's good. Saturday's good.
- I can spend a week in 1955. I can hang out. You can show me around.
- Marty, that is completely out of the question.
[...]