The meaning of on-time performance depends on who you ask. Amtrak defines on-time performance using a minutes late threshold that varies by length of the route. But if you're a traveler, 20 minutes late may be a huge deal, or not matter much at all-- it all depends on the purpose and length of your trip, and the flexibility of your plans.
This is a challenge more broadly: internal agency performance measures do not always map to the aspects of performance that driver user behavior and ultimately the broader effects on society and the economy. Both sides of the coin are critical to our ability to prioritize improvements.