For those who may not have software installed to change computer clock, and for anybody wishing to learn about the history and science of time, go to
http://www.boulder.nist.gov/timefreq/

There are all kinds of goodies here, including if you want it a free program for setting computer clock, and updating it prn.
If you don't do anything else, in left hand column, click on A Walk Through Time. Sensationally interesting.