The default DatabaseCleanupInterval varies based upon the installed operating system.
My Windows Server 2003 DHCP server deletes expired records every 24 hours (1440 minutes).
Using REG.EXE, built into Windows Server 2003, or installed from the Windows 2000 Support Tools, you can set the number of minutes between purges of the expired records from the DHCP client information database:
1. Open a CMD.EXE window.
REG ADD HKLM\SYSTEM\CurrentControlSet\Services\DhcpServer\Parameters /V DatabaseCleanupInterval /T REG-DWORD /F /D Minutes
and press Enter, where Minutes is the number of minutes between purges of expired records.