When creating or editing an event, you have the option to schedule your ticket sales, allowing you to control when they will go on sale and when the sale of tickets will stop.
This can be done in the Edit event page (click on My events, find the event and click on Edit).
Scroll down to the Ticket Type Section and click on the Advanced Options cogwheel symbol to the right hand side of your created ticket, and you will be presented with a set of advanced ticket-selling options.
You can then specify the Start and End time/date of your ticket sales.
If you do not choose to edit this information yourself then the tickets will go on sale as soon as you Publish your event, and the sale of tickets will be scheduled to end at the event start time.