Hyphenated if used as a modifier. I start and finish work late so I can avoid rush hour. It would normally take me about 15 minutes to drive there, but during rush hour, it can take 45 minutes or more. You'd better leave soon if you don't want to get caught in rush-hour traffic.

Is Rush Hour one word or two?

A rush hour (American English, British English) or peak hour (Australian English) is a part of the day during which traffic congestion on roads and crowding on public transport is at its highest.

Is Rush Hour a compound word?

* Rush hour is a compound noun, where 2 words go together to make one noun.