If it's more than 60s or 90s, depending on whether the microwave starts when you hit +30s, you just use the actual time, which is usually 4-5 button presses including hitting start.

For many things, I agree that dials are the easiest. The only downsides are needing to be careful if you want exact times and not having adjustable power levels. A microwave with a dial for power would be awesome though.