How long is a day?

It’s however long your car rental company wants it to be.

That’s what Peter DeForest, a risk management consultant from San Francisco, discovered when he picked up a car from Hertz in Austin recently. A flight delay had made him three hours late to the rental counter. He asked if the agency could adjust his rate.

“They said the charges couldn’t be refunded for any reason,” he says. “So Hertz has a 21-hour day.”

Sorta. A look at its rental terms, which DeForest agreed to when he booked the car, confirms it: There are no refunds for unused days, or for that matter, hours, on prepaid vehicles. A Hertz spokeswoman told me as a matter of policy, cars are rented by the day. DeForest could have brought the car back after only an hour, but he still would have paid for a day.

Hertz is hardly alone. Across the travel industry, companies are adopting clever definitions of everything from “day” to “year” — all with the apparent intent of keeping your money, or just bringing in a little more. No surprise that they’re doing it now, when travel spending is circling the drain. But it’s a little unsettling to their customers that they’re doing it with practically no disclosure.

Take what happened to Ronald Di Costanzo, a retired college professor from Santa Monica, Calif. When he canceled a United Airlines flight a few months ago, a representative told him he had “one year” to rebook the ticket and use the credit. But when he phoned the airline a few months later to reuse his credit, an employee told him his credit had expired.

“I am sure I didn’t talk with the entire Indian subcontinent, but I came close,” he told me. “First, I asked for a supervisor; next, I was asked if I wanted a supervisor; third, I was passed off automatically to another supervisor. All said the same thing, although in increasingly dogmatic terms.”

United offered him a $25 coupon for the trouble, but kept the $392 credit.

Want me to go on? I could tell you the story of Larry Thompson, who lost his ticket credit on American Airlines after one year was abbreviated to nine months. But I’ll spare you.

How do you stay safe from these time bandits?

No guessing games
It used to be a given that a hotel’s check-out time was at noon and that you had a year from the time you canceled your flight to rebook your ticket. And even when it wasn’t, you could usually talk your hotel or airline into letting it slide. Not anymore. Hotels are moving their mandatory checkout times to 11 a.m. (and even earlier) while airlines are strictly enforcing the one-year-from-the-date-of-the-booking rule, when it comes to credit. My point is, you can’t guess what the rules are based on past experiences. In fact, you can check into a hotel at 6 p.m., but if you stay past noon the next day, you could face a late checkout charge or, in extreme cases, have to pay for another day. Ditto for airlines. You have one year from the day you bought the ticket, not the day you were supposed to fly.

Talk is cheap
It used to be that when a reservations agent assured you that you had a one-hour grace period for your car rental, you could be reasonably assured that you’d actually have a full hour. But what do they know? Some car rental companies have shortened their “hour” to 29 minutes; others have done away with it altogether. Are reservationists lying when they claim you have an hour? Not necessarily. Some may not be aware of the changes. Others just don’t speak English, and may be agreeing with everything you say, since there’s no script for them to read. Bottom line: You can’t trust anything an employee tells you by phone or in person. If you’re told that you have a year to use your credit, get it in writing.

Even the written rules can be slippery
If you can’t trust your own experience, or the word of an employee, who can you rely on? I would advise you to review your contract — either the one that came with your ticket or the one on an airline, car rental company or hotel’s Web site. I might be wrong, though. Travel companies don’t like to honor their old contracts when they change the rules. Consider what happened to Delta Air Lines when it updated its luggage rules retroactively, forcing customers to pay $25 for the first checked bag after they had already paid for their flights and agreed to the old rules). When a company doesn’t play fair, your only choice is to appeal to the government or to take the company to court. But normally, having a copy of the contract is enough to prove you right.

I wish I could say this was a new problem, but it isn’t. A decade ago, one of my readers caught American Airlines closing its cabin doors early and refusing to allow him on the plane. Of course, airlines want it both ways: They want to leave whenever they want and they also want to define “on time” in a very un-American way. They’ve managed to persuade the federal government that a flight is “on time” if it’s within 15 minutes of its scheduled arrival time.

Try showing up for a date 15 minutes late and reassuring your sweetheart that the government still considers you “on time.” (Please tell me how it goes. My contact information is listed below.)

Even though some travel companies have a distinguished record of fudging their numbers, this is a particularly bad time for travelers to be caught on the wrong side of the clock. Sure, you can do all the due diligence — research the rules, don’t believe anything that an employee tells you and travel with printouts of your contract — but it’s hardly assuring when you know many travel companies are out to get you.

No wonder that more of us are staying home. This is no way to travel.