By default the windows time server updates once per week.

To change this time you will need to edit the windows registry and change the following setting:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\W32Time\TimeProviders\NtpClient

has a value SpecialPollInterval update this to a value greater than 1 in milliseconds.

To put this into effect press update now under Date and Time > Internet Time > Change Settings > Press Update Now