Because cutting time is only a fraction of the total job.

A job might be on the machine for 20 minutes, but if it requires careful setup, repeated checking, manual intervention, deburring, sanding, or fixing small issues, the real time cost balloons. What looks efficient on a screen often isn’t efficient in reality.

Experienced workshops measure time from the moment material is loaded to the moment finished parts are stacked. Anything outside that window still counts — even if the spindle isn’t turning.