ducks back down

[Topstudent]

I'm writing a script:

John is hiding behind his car. He waits a long moment, then cautiously peeks over the hood and sees the gunman looking his way. He quickly ducks back down. Thinks.

Does 'ducks back down' seem okay here?

 

[emsr2d2]

Yes.

What's a "long moment"? The general idea of a moment is that it's short.
I'd use "but sees the gunman". That gives the idea of cause (seeing the gunman) and effect (ducking back down).
I don't like "Thinks" on its own. I'd say "... ducks back down and starts thinking".