Is it possible to finish 18 holes in less than 4 1/2 hours if you start round early enough?

Yes but you have to be out early...break of dawn

Maybe at midnight.

Like others said, you have to start really early. If you must finish in less than 4.5 hours, you have to be the first one out. Otherwise, you are at the mercy of groups in front of you.

HIGHLY doubt it, unless you're on dawn patrol.

Yes. Be the first time out.

Yes, but you need to start EARLY. One of the first few groups out after sunrise.

Sure...