Your tickets availability is controlled by two main factors:
1. General box office availability
2. Each individual ticket start / end dates.
Of course, there are additional nuances such as ticket limits but the dates are the most important ones to control what is available when.
General box office availability
Once registration is configured, go ahead and enable it. You can always disable it if necessary. As soon as you enable your registration, your sales are now open. You can specify overall sales end date in the Edit Registration section.
Scroll down to Ticket Sales End section. There you can specify when you want your box office to close.
Individual ticket start / end dates
In addition to the overall box office dates, you can control when each individual ticket is available. You can specify ticket end date (as in a case of Early Bird tickets) or a delayed start date (eg: Regular Price ticket starting after Early Bird)
In order to do that, navigate to the Tickets tab in your registration configuration and select the ticket you want to edit. There you can specify when you want this individual ticket to be available by selecting start and end dates. Both of the start / end dates have a few options to allow a very granular configuration for ticket availability.