Apply Group Policy for users asynchronously during logon
Computer Configuration\Administrative Templates\System\Group Policy
Lets the system display the Windows desktop before it finishes updating user Group Policy.
If you enable this policy, the system does not coordinate the tasks of loading desktop and updating user Group Policy. As a result, Windows might appear ready for use before user Group Policy is updated.
If you disable this policy or do not configure it, the system does not make the desktop available to users until user Group Policy is updated.