You can find the exact expiration time of a Set Award within the Set (in both screens 2 & 3).

 

The Award Rewards In time will let you know when the Award is scheduled to be delivered to qualifying users.

 

Once the Rewards In time passes the Award will become expired and can no longer be earned by collecting the required cards. 

 

Users that have not completed the required collection will not be eligible to earn the Award.