You may or may not be aware that when you are booting a virtual machine under Virtual PC or Virtual Server you can press the Del key to enter the virtual machines bios. The first configurable option that you’ll see in the bios is the System Time and System Date. You can easily change these values, however there is no point. You see, the virtual machine will be rebooted after any Bios changes are made (this is standard behavior for computers) and when the virtual machine reboots its system time and date will be automatically reset to match those of the host operating system.
P.S. Occasionally we get requests cannot override the system time when the virtual machine is rebooted. But the reality is that the host operating system time is the most accurate value that we have to use for the virtual machine time when booting the virtual machine.