Make following registry change on Windows NT server to act as a time server:

Hive: HKEY_LOCAL_MACHINE
Key: SYSTEM\CurrentControlSet\Services\LanManServer\Parameters
Name: TimeSource
Type: REG_DWORD
Value: 1
See:
W32Time Network Time Service For Windows NT 4.0
Q174557 - Time Sources Defined For The Windows NT Time Service.
Q131715 - How to Set Up And Synchronize with Domain Time Source Servers.
Q193825 - NET TIME /Domain Will Not Sync Time with Domain Time Source Server.
Q172831 - TimeServ Uses 100% of System Resources .
Q172878 - Resource Kit Timeserv.exe Utility Causes 100% CPU Utilization .

For Windows NT client computers, type the following in the MS-DOS Command Prompt or add the following to the login script:

NET TIME /DOMAIN: /SET

For Windows or MS-DOS based client computers, such as Windows, Windows for Workgroups, LAN Manager for MS-DOS or Microsoft Network Client for MS-DOS, type the following in the MS-DOS command prompt or add the following to the login script:

NET TIME /WORKGROUP: /SET

If your interest is Windows 2000, see my tip Windows 2000 Admin Tip #47: W2K Time Synchronization service.