hour (time period of sixty minutes) / o'clock / hour (season, moment, or time) / lesson of forty-five minutes

curfew (a regulation requiring people to be off the streets and in their homes by a certain time)

(idiomatic) what time is it?

(idiomatic) rainy day (period of need or difficulty)

(historical, World War II) "W" Hour (codename for the date and time that began Operation Tempest in German-occupied Warsaw, and hence the Warsaw Uprising) / (figuratively, by extension) high time, zero hour, H-hour (time when something important will happen)

(idiomatic) zero hour