In Windows 2000 AD, once a DC gets a modification, it sends out a notification to its closest replication partner 5 minutes later, and send the subsequent notifications to the other replication partners with 30 seconds pause.
If you change the forest level to Windows 2003, the numbers change to 15 seconds and 3 seconds respectively.
These values are stored in the following registry:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NTDS\
Parametersms\Replicator notify pause after modify (secs)
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NTDS\
Parametersms\Replicator notify pause between DSAs (secs)
In AD, you can find the value on the cross-reference object for each directory partition in the Configuration container.
DSReplicationNotifyFirstDSADelay
DSReplicationNotifySubsequentDSADelay