The Van Horn date/time are based on the time in your computer and the relative time to Van Horn itself.  What that means is that if your computer time is not accurate for your location then the Van Horn time will also not be accurate.  You should check your computer clock regularly and even use a time synchronization program to set your clock if necessary.  A simple search of the Internet will produce such software.  There is a site at http://www.eecis.udel.edu/~ntp/software/index.html or http://www.ntp.org along with other sites that have such software available.  Most of these programs poll the current time information from the Atomic Clock in Boulder, CO.