I was a bit puzzled by the fact I could not easily change the date/time in an instance of a virtualbox as used by the High Performance Scientific Computing Coursera course run by Dr. Randall J. LeVeque via Coursera.
I tried using the simple
date command but I kept on being told that
date: cannot set date: Operation not permitted
I tried updating the Ubuntu distro, but no luck. Eventually I found a solution using a symlink to localtime:
mv localtime localtime_original
ln -s /usr/share/zoneinfo/Europe/London ./localtime
You will have to use the correct zone for your location. Et voilà!