A. Policies are refreshed every 90 minutes (5 on DC's). To force a machine to update the policy use the SECEDIT command.
To update the computer policy type
C:\> secedit /refreshpolicy machine_policy
To update the user policy type
C:\> secedit /refreshpolicy user_policy
Adding /enforce to any of the above forces a reapply of the security policy even if there is no GPO change.