(Bloomberg) — If Walter Robb went on vacation today, he wouldn'thave to be back at work as co-chief executive officer of WholeFoods Market Inc. until about March–of 2017.

Robb has accumulated 2,703 benefit hours–better known as paidtime off–since he joined the grocery-store chain in 1991.

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Chopped into 8-hour shifts, they add up to 338 days, which hecan take in time or cash.

While Whole Foods is the rare U.S. company that letsemployees roll all their vacation overyear after year, Robb's not unusual in his aversion to actuallyusing it.

Proxy filings tally untouched vacation time. StevenMollenkopf, CEO of Qualcomm Inc., has had at least $121,000 inaccrued vacation pay at the end of each fiscal year since 2010. HCAHoldings Inc.'s R. Milton Johnson had $152,308 at the end of2014.

Apple Inc.'s Tim Cook was reimbursed $56,923 in 2014 for unusedtime.

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“With technology today, forget it–you're never off,” said JonLuther, former CEO of Dunkin' Brands Group Inc., who did takevacations but would spend mornings on work calls before switchingto relaxation mode.

It's dangerous not to schedule downtime, he said. “You've got tomake sure that you step away from it on occasion to draw a deepbreath and get your batteries recharged.”

It should be easy to totally tap vacation time in the U.S.,because there's so little of it, relatively speaking. Americanemployers typically mete out between 15 to 25 days a year to topmanagers, based on a survey by executive coaching company VistageWorldwide Inc.

Laws in countries including the U.K. and Sweden require that allworkers get about five weeks.

In fact, the U.S. is the only advanced nation that doesn'tmandate paid leave, according to a report from the Center forEconomic and Policy Research.

That, coupled with bosses who rarely go on breaks, can create a“culture where employees feel insecure about taking vacations,”said Eden Abrahams, managing partner at Clear Path ExecutiveCoaching.

A handful of U.S. businesses go to another extreme: unlimitedvacation. That means workers can take as many days as they like —or dare. Netflix Inc. introduced the policy in 2004 and others inSilicon Valley, including Uber Technologies Inc. and Reddit Inc.,have adopted it. Netflix CEO Reed Hastings told an audience at theNew York Times Dealbook Conference in November that he takes offabout six weeks a year and is “open about it internally to try toset a good example.”

At Whole Foods, each of the seven top executives — includingco-founder and co-CEO John Mackey and Chief Financial OfficerGlenda Flanagan — had more than 1,200 hours of accrued time off asof September last year, according to its most recent proxyfiling.

The amount “they have accumulated is, in large part, areflection of the decades they have dedicated to serving WholeFoods Market,” Michael Silverman, a company spokesman, said in ane-mail. Spokesmen at Qualcomm, HCA and Apple declined to comment ontheir executives' vacation time.

Whole Foods employees have the option of cashing their time outat 75 percent of accrued value once a year or collecting the fullsum when they quit.

“If your top guy walks away with a couple of hundred thousanddollars of unused paid time off, that probably sends a message toother people within the organization: 'That's what we shoulddo,”' said Michael Molina, Vistage's chief human-resourceofficer.

Executives have a responsibility to be role models, he said,which is why he tries to use all his four weeks of annualleave.

Certain situations, such as being new on the job or leading aturnaround effort, could make it impossible, or unwise, for someoneto dip into the time-off pot, said Luther, a director at Six FlagsEntertainment Corp. since it emerged from bankruptcy in 2010. “It'san ongoing discussion on compensation committees to make sure thateverybody isn't burnt out.”

When Colin Hall, chief marketing officer of shoe retailer AllenEdmonds Shoe Corp., went to Hawaii with his family in 2010, helogged on in the wee hours and shut down before noon. “I felt likeI worked a full day but then the afternoon and evening was totallyfree,” Hall said. “I was literally guilt free.”

At a small company, it can be hard to disappear. Deb Erickson,founder of The Line Up, which makes cheerleading costumes for theMinnesota Vikings and Baltimore Ravens football teams, said she'slucky to get away for just a couple of weeks because there aren'tmany on staff who can fill in for her.

Erickson doesn't have any vacation plans at the moment, but shecan dream.

“I think I'd go somewhere in Europe,” she said. “Someplace farenough that no one can really get to you.”

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