Before purchasing an e-ticket you can select the date and time at which you want to travel. Although the ticket does not need to be activated it is only a valid way to travel on the specified date and time, visible on the ticket itself.
You can view your tickets in the Gaiyo dashboard or by tapping the menu in the top right corner and tapping "Tickets & Reservations". The date and time should be visible on the ticket behind: "Valid until".