The National Institute of Science and Technology (NIST) provide accurate time servers that you can synchronize your system with. In LabVIEW, you can poll the information from the server via TCP and then use the kernel32.dll to appropriately set your system clock. The code below demonstrates this behavior. A full listing of all the available time servers can be found here: http://tf.nist.gov/tf-cgi/servers.cgi and more information about programmatic control of Windows can be found here: http://en.wikipedia.org/wiki/Windows_API.
Verne D. // Software R&D // National Instruments