What is the origin of the idiom "a day after the fair" and when to use it?

The idiom "a day after the fair" is believed to have originated from the context of fairs and carnivals. In the past, fairs were significant events that attracted large crowds and offered various attractions, entertainment, and commercial opportunities. The phrase conveys the idea of arriving or taking action after the fair has ended, indicating that one has missed out on the excitement, benefits, or opportunities associated with the event.