Thanks for the insightful response.  I think the right solution for my scenario would have to have the VM manager intelligent.  The VM itself would never "automatically" sleep based on time settings in the guest, but when the host sleeps it would broadcast WM_POWERBROADCAST within the guest OS.  This would give guest apps the opportunity to respond and register sleep wake events.  Those sleep wake events end up in the guest BIOS, which the VM manager is running.  The manager can then forward those sleep wake events onto the host OS.

The thing is, I can easily write an application which is smart enough to forward WM_POWERBROADCAST.  However, the VM Manager would have to have some support for the sleep wake events as they appear in the VM BIOS.