Without a domain, you can’t setup an authoritative time server so you can synchronize your machines using 3rd party software. Usually you can get this for free. You can try Atomic Clock Sync.
You can set your system to synchronize from NTP source(s). No third party software required. You must allow NTP through the firewall(s) on your network.
As an alternative, you could add a third party NTP service to your servers and use them as an NTP source.
A quick example script to setup NTP on a Windows XP system.
REM Ensure the time service is setup on the client
REM Set the client to client mode only!
REM Microsoft default is to as time server as well!
REM This can cause issues on your network.
REG ADD “HKLM\SYSTEM\CurrentControlSet\Services\W32Time\Config” /V “AnnounceFlags” /T REG_DWORD /D 0 /F
REM Set the service to auto start
SC config W32Time START= Auto
REM Start the service
SC start W32Time
REM Set to sync with NTP server(s). Set your choices here.
W32TM /config /manualpeerlist:”time-a.nist.gov time-nw.nist.gov” /syncfromflags:MANUAL
REM Force a sync update
W32TM /config /update
REM Restart your system for all changes to take affect.