For a commuter rushing to catch a train, a minute can mean the difference between dinner with the family and leftovers in the microwave.

What most passengers do not realize is that their minute is already there.

Every commuter train that departs from New York City  about 900 a day  leaves a minute later than scheduled. If the timetable says 8:14, the train will actually leave at 8:15. The 12:48 is really the 12:49.

In other words, if you think you have only a minute to get that train  well, relax. You have two.

The phantom minute, in place for decades and published only in private timetables for employees, is meant as a grace period for stragglers who need the extra time to scramble off the platform and onto the train.

“If everyone knows they get an extra minute, they’re going to lollygag,” explained Marjorie Anders, a spokeswoman for the Metro-North Railroad. Told of this article, Ms. Anders laughed. “Don’t blow our cover!” she said.