Summary: Time is an important design variable to understand. Time or temporal aspects of tasks hide metaphors, flows or triggers that you can bring into your deisgn. Designs that miss out on the time aspect of Interaction Design face a poor or failed user experience.
Examples of Time in Design
1. Pizza ordering: Domino's uses the time tracker as a way to manage expecations.
2. Ticket-ordering: TicketMaster and others use the countdown timer to secure the purchase (and refresh inventory).