Highlights of this feature:
The number of days from the beginning of the listing until upgrade ability is removed from a specific listing is set here in the admin tool:
LISTING SETUP > GENERAL SETTINGS > UPGRADE PERIOD
As seen in the following screenshot:
The number of days from listing start the upgrade is available is a site wide feature that affects all listings that can be renewed. If the above is more than 0 (set to 0 to disable) that will allow upgrading to any listing type in the system.
Additionally you have configurations to additionally affect this feature on a price plan by price plan basis. Within the Listing Renew/Upgrade price plan item there is an additional setting as shown in the following screenshot:
The above allows you to reset the start AND end times of the listing after a listing has been upgraded.