I have a stupidly cheap microwave which I bought a few years ago (because I moved homes and the last one, a rental, included a microwave) and it has no clock.

In fact, it doesn’t even have the simplest of displays - the entire user interface is one analog rotary control for power and another for microwaving time - the latter rotating back by itself at a fixed speed - plus a bell that dings when the second control reaches the zero position.

If I want to know how long till a microwaving operation is finished I just look at the position of the second rotary control.

Sometimes simpler is better.