You can set an expiration date for each App on your CMS by clicking on the Time button from your App list:
You can set it for 30 - 60 or 90 days (or set no time limit at all):
You can change this setting at any given time.
You can also set Advanced options for your expiration date by clicking on the Options tab on the left from your Dashboard App list page:
And then inserting the relevant information from the Advanced panel: