You can now view and update current assignment expirations for your permission sets and your permission set groups. Previously, to update assignment expirations, you recreated them with the correct expiration date.
Where: This change applies to Lightning Experience and Salesforce Classic in all editions.
Why: Suppose a sales manager wants consultants to evaluate the language used in sales contracts. You give the consultants access to the contracts object and other permissions via a permission set group so that they can perform their work. The project has an end date, so you don’t want contractors to access sales contracts after that date. Set the expiration date for the permission set group when you assign it to users. If the project end is extended, edit the expiration date for the permission set group to the new date.
How: Enable Permission Set Group Assignments with Expiration Dates (Beta) in User Management Settings. Then from either the Permission Set Group or Permission Set page, click Manage Assignment Expiration. On the Current Assignments page, you can view a list of the users that are assigned to the permission set or the permission set group. To create a user assignment, click Add Assignment. To modify the expiration date of existing assignments, click 
. To remove an assignment, click 
.
Manage Assignment Expiration in Permission Sets and Permission Set Groups (Beta) (salesforce.com)