In order to set when the sales end for your event, follow the steps:
Go to the "Administration" tab
Click on"edit" under the "plays" section.
Select the play you want to edit from the events list on the right-hand side of the screen
Click on the "existing events" tab.
In the "ticket presales end" column you can see how long before (or after) the start of the event will online sales end. This is displayed in the following format:
Day : Hours : Minutes : Seconds
To change the end of sales time, select the specific event date in question (click the tickbox next to the venue's name) and then click on "end of ticket presale" at the bottom of the screen.
Select if the sales will end before or after event's start time and then set the days, hours or minutes you want from the dropdown menu. Click "save".