I accidentally discovered that microwave timers are kind of interesting. I've checked this with a few microwaves I've had, and they've worked this way. My present one is a Sharp.

If you enter 59, you get 59 seconds.
60 gives you sixty seconds.
99 gives you 99 seconds.
100 gives you 60 seconds.
160 gives you 120 seconds but it counts them as 60, two times.
199 gives you two minutes and thirty-nine seconds. (Just verified it.)

Also, it you want a minute and a half, it's easier to punch in 99, and be 9% over, than to punch 1, 3, 0.

For that matter, I usually punch in 33, not 30. I reheat a cup of coffee with 88 when I first worked out that 90 seconds (or 1,3,0) worked right. Same button twice is quicker and easier than two different buttons. It's also 10% over the two buttons, but cooking times are always approximate anyway. Ratios of ingredients matter a lot, but times a bit less so.

To heat the water for my coffee, I don't hit 4, 0, 0, Start. I hit +1 minute, four times. Same button four times instead of a mixture of three buttons.

Does your microwave do any of this stuff?