I can't think of anything that quite fits that off-the-cuff, at least not in the US. A quick search doesn't turn anything up. I can think of some related things:

• The AC signal is used as a clock in a number of devices. This isn't a "clock" in the common-language sense of the word, but in the electrical engineering sense -- it provides a reliable frequency over the long run. Some (common-language) clocks and timers have used this to keep them running at a steady pace, but it's not really a time signal, wouldn't help restore an on-device clock setting after power loss.

• X10 is a low-speed networking protocol that runs over local power circuits for home automation. I'm sure that at some point, someone has made some product that permits setting a clock with it. The limitation is that your signal doesn't span across household circuits, which I suspect one would want for a "whole house time signal".

• There have been powerline-based ISPs, where the power company shovels data over the line using high-frequency modulation. In theory, you could use one of various Internet time protocols over that. I think that that was kind of a dead end, technology-wise

there's just not that much data that you can push over an unshielded, non-twisted-pair, metal power line.

• I would not be surprised if there's some data protocol that power companies use to talk to smart meters that includes pushing a time signal out specifically for them -- they do push and pull data over that -- though I don't think that that's accessible to other devices.

That being said, could be some company out there that did that locally. Not technically impossible.

looks puzzled

Hmm. What are you doing with that? Like, you want to be cooking for a certain amount of time, then after the cooking completes, have a timer trigger to start a second cooking period?