Sometimes you need to allow athletes in one registration class to be able to edit their registration details for different time periods than athletes in other classes.
You can set this up in the class editor. Here's how:
From your dashboard, click the red edit link to the right of your event name
Click the Classes + Categories link on the left sidebar
Click the red edit link next to the class you'd like to change or add a new class
Scroll to the bottom of the class editor and make your selection next to "Allow participants to make changes to their registration details until ___ days prior to the event." Pick the number of days from the drop down menu