Set date and time on virtual machine independent of host machine

Our setup is a Debian guest with VirtualBox on an Ubuntu host, but the two basic steps look like they are the same on any combination.

Shut down all virtual machines and close VirtualBox first.

To the main VirtualBox configuration file — ~/.VirtualBox/VirtualBox.xml — and to the specific virtual machine's configuration file — something like ~/VirtualBox\ VMs/somename_default_1415392315537_7406/somename_default_1415392315537_7406.vbox — add the following, identical line into the existing <ExtraData> sections:

      <ExtraDataItem name="VBoxInternal/Devices/VMMDev/0/Config/GetHostTimeDisabled" value="1"/>

Courtesy page two of the forums.virtualbox.org thread "How to disable time sync between host and guest".

And then in your virtual machine set the date and time with the date command:

     date --set 1998-11-02
     date --set 21:08:00