an hour is a unit of time, typically denoting the length of 60 minutes. When used as a noun, the word 'hour' refers to the actual length of time being measured, or it can describe a particular point in time of day, such as noon or midnight.
generally, the word 'hour' is used to describe a specific unit of time when telling the time of day, or the length of time of an event or action. It is also commonly used to refer to something or some activity that happens periodically or repeatedly after set intervals.
1. I get off work at five o'clock in the afternoon.
2. We will have to wait at least an hour before the meeting starts.
3. She is usually diligent about getting her workout in for an hour each day.
as a noun, it is important to remember that 'hour' requires a determiner (like 'an' or 'the') when used in a sentence. Furthermore, when talking about long periods of time, 'hours' is the correct plural form. For example, 'I was stuck in traffic for three hours'.