On the Event Settings tab at the top of the page you can enter the Event Starts On and Event Ends On dates and times. You can type in the information or use the calendar icon to select the date and the clock icon to select the time. 

The Online Sales Starts On and Online Sales Ends On dates are the dates that the page will be visible to the public. Outside those date, the public will see and error message as shown in the Message to Display When Online Sales Are Not Active. 

After the page is created, the calendar icon can no longer be used to extend the date without deleting the Event Ends On date and the Online Sales Ends On date and saving the page. Once those dates have been deleted, you are able to use the calendar icon again or the dates can be manually updated.