Once tickets created for event, you can setup Ticket Selling Dates and point as Online or Box-Office for each ticket.
- Click on "Ticket & Add-on" from the left side event menu to go to Manage Tickets page
- Now,if tickets are already exist there will be ticket listing row for each ticket
- Click on 
(Settings icon) located on the right of ticket row to open hidden ticket option
- On this window see and check the box for "Ticket Selling Duration" will allow to start and end date field
- Now set "Start Date & End Date" with the date picket calendar to set selling duration
- Also, find option "Selling Point" and check the box for "Box-Office" and /or "Online" to set ticket selling point
- Once done close the window to go back to Manage Ticket page
- Click on "Save" to apply changes
- Please note ticket level "Selling Duration" will be apply within event level "Ticket Selling Date" range
All good!