60Hz - > 16.6 ms period time. So 3-5ms switching time will not noticed by 99.99% of home equipment. But do not mix relay/contactor switching time with system transfer time (time between power failure and switching complete). Some system may be slow on power failure detection. Actually most of home electronic/electric devices will work without interruption if complete switching time is below 200-300ms.
It also depends on where on the AC voltage wave cycle when switching happens which is likely random for power outages.