Ben Armstrong has saved us all several agonizing hours with this great, simple blog post about how to disable time synchronization in Virtual PC. In short, the process entails opening the .vmc file and updating the enabled flag to "false" within the host_time_sync element:
<host_time_sync>
<enabled type="boolean">false</enabled>
</host_time_sync>
Fortunately, disabling time synchronization in Hyper-V is as simple as clearing a check box. Right click the VM in question, select Settings, and choose Integration Services under Management. Next, simply clear the "Time synchronization" feature and hit OK:
When might you want to disable time synchronization? Ben's post got me out a bind once when doing a presentation on a VPC OS that was about to brick due to expiration lockout. Brian Keller, Developer Evangelist at Microsoft points out some tips for beating CTP expirations here. In my case, I converted the VS 2010 .NET 4.0 VPC to Hyper-V which Grant Holliday captures well here.
Of course, I do not recommend or advocate this as a means to cheat or steal, but it may come in handy should the process be sanctioned by the particular software vendor.
Hope this helps!