Make WinXP’s NTP client poll more frequently (hourly)

At the registry key:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W32Time\TimeProviders\NtpClient

Change the value SpecialPollInterval to 3600

3600 seconds = 1 hour

Save and restart the Windows Time service:

net stop "Windows Time"
net start "Windows Time"

Taken from: http://dossy.org/2007/02/make-winxps-ntp-client-poll-more-frequently/