NEW YORK (MainStreet) — Although everyone needs the occasional midday break for running errands or popping out to a doctor's appointment, vanishing from the office regularly for two or three hours at a time can mean getting passed over for promotion, ignored for special projects or fired — sometimes without warning. Our experts weigh in on the hefty consequences of lunchtime disappearing acts and the best ways to handle those times when you need to step away without taking a vacation day.

Sometimes I need to get out of the office for an extended break. How do I know when I'm crossing the line?

"Occasional long lunches are very acceptable. Everyone has something they need to take care of during the day. But when you disappear for two hours and come in loaded down with shopping bags or sporting a fresh pedicure, then it's a problem," says Elaine Varelas, managing partner at career management consultancy Keystone Partners.

It really comes down to understanding your company's workday philosophy, says Amanda Augustine, job search expert for job matching site TheLadders.

"A young startup will likely want you spending as little time out of the office as necessary, since teams are lean and workloads are heavy," Augustine says. "A more established organization may be more open to longer breaks, especially if your work is less time sensitive."

Additionally, some companies or departments value "face time" more than others, which affects their view of extended lunch breaks, Augustine says.

"If you're new to a company, make friends with someone who's been with the organization for a while and can clue you into the unwritten codes of conduct," she says. "Don't be afraid to bring this question up to your manager when you're discussing his or her expectations of you on the job. There's nothing wrong with finding out what's considered an acceptable lunch break and what isn't."

If I have to go out, should I sneak out of the office or announce that I'm leaving?

It's always best to be upfront and honest about where you're going and when you'll be back, Varelas says.

"Even if you think your bosses aren't watching, they are. Every time you disappear without warning, there's a chance someone will start looking for you. If they can't find you, they can't depend on you, and that's dangerous," she says.

Employees must communicate their schedules to management, and always notify them when there are personal matters that will take precedence over work priorities, such as an ill child or parent or doctor appointments, says Steve Moore, director of human resource operations at HR consultancy Insperity.

If you have to step out for an extended period, make sure you're "wired" if anything big comes up, Moore adds.

"Employees should use portable technology — such as smartphones and tablets — to stay organized and maintain productivity when they are out of the office," he says.

Will I be more likely to get promoted if I never leave my desk?

"Absolutely not," Varelas says. "Good managers want their employees to leave the office, go for a walk, eat something healthy. Lunch breaks are mental health breaks, and everyone should have them."

Taking a lunch break can absolutely recharge you, says Tracy Cashman, partner and general manager of information technology search at recruitment firm WinterWyman.

"During lunch, some people take a walk, others go to the gym, some socialize in a common area, and some eat at their desk and read the paper," Cashman says. "Any employer would vote for an employee who takes a 30- to 45-minute lunch break and then spends the rest of the day being productive."

My bosses and colleagues step out for long lunches. Am I safe if I keep the same schedules they do?

The "rules" on lunch breaks — written and implied — not only vary from company to company, but also from department to department, Augustine says.

"For instance, there may be a lot of latitude for a midlevel sales professional whose only goal is to hit a certain quota, whereas an hourly worker in a call center will most likely have to comply to more rigid lunch-break rules," she explains.

At no point should you think that long breaks are OK just because others are taking them, Varelas says. The others you see going to lunch may have a standing weekly meeting to attend, but no one will know where you're headed.

"Your absences will be cause for concern. Your colleagues and managers don't anticipate that you're at the gym. They think you're at the bar, or another job interview," Varelas explains.

If my boss hasn't complained, then I'm OK, right?

Your boss may not have given you a formal warning or even seemed to notice your long breaks, but your actions will come back to haunt you, Varelas says.

"It's going to come back around at some other time, when you are overlooked for a valuable project, or when your raise is smaller than someone else's — or nonexistent," she says.

Even if your boss hasn't been watching your departure and arrival times, colleagues talk, she says. In many cases, even friends will turn into tattletales.

"If your colleagues feel overburdened or get the feeling that you don't have a conscience or a work ethic, absolutely they will tell on you. Even if they don't do it directly, they will make sure management knows," Varelas says.

Although most often you will get a warning from your boss if he or she is unhappy, sometimes it comes right out of the blue.

"If they see a steady habit that's totally unacceptable, there may not be a warning. You'll walk in one afternoon, and that's it. You're fired."

What if I really just can't stand being at my desk for more than four hours a day?

Even if you're unhappy, taking advantage of the company by leaving to spend three hours at a shoe sale is not the way to handle things, Varelas says. If you're really that miserable, it's time to look for ways to improve your situation.

"Evaluate why you're unhappy," she says. "Perhaps this is a temporary feeling and you just need some vacation time, or maybe you need to be reassigned to a different project. But if everything about your job is negative and you don't enjoy anything, then it's definitely time to change roles, change companies."

— By Kathryn Tuggle