This security setting determines the maximum amount of time (in hours) that a user's ticket-granting ticket (TGT) may be used.
Computer Configuration\Windows Settings\Local Policies\Kerberos Policy
clients will get the new setting after a maximum of 8 hours but for DCs to assign these new settings a Gpupdate /force is required or waiting for the usual 5 minutes when the SCE engine assigns all modified settings.
At least Windows XP SP2, Windows Server 2003
Kerberos Policy security settings are not registry keys.