This is why I have box mixes in hand for cooking when high, I've made them so often I don't mess them up. And there's always a non high person around in case I don't hear the timer go off for the oven.
A big oven doesn't work with just a timer, because even if it turns off it will continue cooking. A small convection toaster oven or instapot can turn off and the heat evaporates quickly, so you can just leave it and it won't burn.