Two rotary knobs for selecting power and duration and two push buttons for start and stop.
Actually a third push button is also required, for storing a power+duration pair, when you want to have multiple segments where different powers are used.
When using a microwave oven for cooking, not just for reheating, it is very common to use a high power for a short time, then one or two decreasing power levels sufficient to just preserve the current temperature, in order to avoid making a mess in the oven, due to violent boiling or high pressure steam generation.
