I have a Samsung 1000W microwave I bought 2 years ago with a big button to add 1 minute to the current cooking time. Each time you hit it, you add 1 minute. It is very handy.

My Samsung (M6245) bought more like seven years ago has the same button. If you press it while it's not currently cooking, it starts up for 1 minute at 100%. I very rarely use any other button except the door-opening one.

Peter