The rush hour is the busy time of day when everyone travels at once. The morning rush hour, avoid the rush hour, rush hour traffic.
It lasts a good deal longer than an hour in any real city, which is the joke inside the phrase. Spreading it out is the cheapest way to add capacity to a transport system, which is why off-peak fares exist.
1phraserush hourThe busy time of day when everyone travels to or from their job at once.
“Try to avoid the Underground during rush hour, when you can hardly move on the trains.”
rush hour is a time.
Practised in In the City, Time & Calendar