To adjust the interval that Windows XP updates the time from the configured SNTP server.
Open the registry editor and navigate to...
HKEY_LOCAL_MACHINE\SYSTEM\
CurrentControlSet\Services\W32Time\TimeProviders\NtpClient
...where you will find the SpecialPollInterval value. Double click it, change the base to decimal, then enter the new time interval in seconds.
The default is 604800 seconds (7 days), unless you are part of a domain in which case the default may well be 3600 seconds (1 hour). Domain members should not change this setting and should not try to use an external time server. Time synchronisation is critical within a domain for security reasons; your PC time will be regularly updated by your domain controller.
To have your clock synchronised every day change the value to 86400 seconds (24 hours)
WARNING: Do not use the registry editor unless you are sure that you know what you are doing. Improper use of the registry editor can cause your machine to become unusable.