To control the number of seconds to wait between attempts to synchronize the system clock to an time source on the Internet using the following Windows XP registry hack:

Hive: HKEY_LOCAL_MACHINE
Key: SYSTEM\CurrentControlSet\Services\W32Time\TimeProviders\NtpClient
Name: SpecialPollInterval
Type: REG_DWORD
Value: #secondsdesired default

Don't set it too low. Your PC clock doesn't drift that fast. Once a day is good enough.

(default) will control which time server to use. The Servers key will have entries for internet time servers. For example my system has (default)=2, value 1="time.windows.com" and value 2="time.nist.gov". Meaning my time is syncronized from the nist.gov site. To control which time source to synchronize the system clock with, use the following Windows XP registry hack:

Hive: HKEY_LOCAL_MACHINE
Key: SOFTWARE\Microsoft\Windows\CurrentVersion\DateTime\Servers
Name: (Default)
Type: REG_SZ
Value: entry of choice, 1-# time servers you have default

If you want to add a new time server, add a new value, in my example the next value 3="thenewtimeserver.com"