Delay Mains power after a blackout
An application for a time delay relay though in most cases you'd need that driving the control/coil of a heavy duty relay/"contactor" to actually switch appliance or whole-house power, as most time delay relays (TDRs) are fairly low current devices. One to switch whole house power will probably be expensive, but one for each circuit will add up, so you'll have to make that call based on what you find when shopping.

TDRs are a standard industrial item, widely available in many configurations. While you may not be aware of them, many consumer devices have one built in (i.e. my air conditioner has to have had power for 3 or 5 minutes (I don't recall which) before it will start the compressor, so that a an outage or being unplugged does not result in trying to start the compressor before it's ready to be started without damaging itself, if it had been running before the power went out.