"The interval at which a group policy is refreshed is defined by a refresh interval value and an offset interval value. The refresh interval is an amount of time between 0 (zero) and 64800 minutes (45 days), which is used to determine when the group policy should be applied next. By default, if the administrator does not modify the default setting, Windows 2000-based computers use 90-minute intervals. For domain controllers, the default is 5 minutes. This default for domain controllers is used because when a change to domain policy or rights is made, this reduces the latency in applying the change to domain controllers as replication occurs. If 0 (zero) is specified for the refresh interval, the refresh occurs in 7-second intervals.
To avoid the performance degradation that can occur if many Windows 2000-based computers request a group policy refresh from domain controllers at one time, a random offset interval is added to the refresh interval to determine the total amount of time between group policy application cycles. The valid range for the offset interval can be 0 (zero) to 1,440 minutes (24 hours). The default for Windows 2000-based computers is 30 minutes, while the default for domain controllers is 0 (zero) minutes."
Microsoft provides instructions on how to modify these defaults in KB article Q203607, "HOW TO: How to Modify the Default Group Policy Refresh Interval"