In this economy, sellers will adjust their prices over the course of the market day to ensure that they dispose of the entire supply that they have brought to market. This was the world in which the early economists like Adam Smith grew up, and these were the arrangements which they reflected in their models of the economy.
It was a quite literal description of the behaviour they experienced every day. The overwhelming proportion of the populations lived in villages in the countryside, their daily activity for most of the week was production and consumption. Trading, that is, economic exchange, took place only on a single day, in a discrete space, for a specified time.