Yes. The crystal in your microwave's CPU clock circuit will drift, and so will the time-of-day derived from it until you set the time again, if there is no ext

Yes. The crystal in your microwave's CPU clock circuit will drift, and so will the time-of-day derived from it until you set the time again, if there is no external reference. The benefit of using the incoming 50/60Hz AC signal as a timebase is that the power station is responsible for controlling the long term frequency to avoid drift so it can be used as a very reliable reference.