NEW YORK ( TheStreet) -- If you're looking to get a small business off the ground, you know just how daunting a challenge it can be. From the long hours to the start-up costs, entrepreneurship isn't easy, and there's always the chance your business could be a failure. For extra stability and cash flow, many entrepreneurs choose to maintain their full-time "day jobs" while launching their businesses in secret -- and it goes without saying that most employers won't be happy if one of their employees is moonlighting with an eye toward leaving the company.

Even if you're careful not to use work time or company equipment in your efforts, experts warn that juggling two jobs is a risky proposition. Going in, it's important to be "very realistic" about the needs of your new business and the needs of your day-to-day job, says Jerry White, director of the Caruth Institute for Entrepreneurship at the Cox School of Business.

"It is easy to think you can do two full-time things and then realize you've gotten yourself into an impossible position," White says. By the same token, "if you don't pay the bills, the whole thing collapses."

Before you begin, considerable thought should go into what kind of business you want to start and what kind of job you currently have, White says. For example, if you travel a lot for work, your new venture must be able to go on hold while you are away. If your business grows to the point that you find yourself filling orders while you're on a business trip or sitting at your desk, that's a problem.

"Using company time is a good way to get fired," White says. "The key is to format your business so that it fits around your day job."

It will become painfully obvious to your supervisors if you're not meeting your job goals or if things start stacking up at the office that you usually can work off, White adds. If you're serious about keeping your current employer happy you'll need to "be your own doctor and read the symptoms," says Marnie Swedberg, founder of B.U.S.Y.: Best Unique Strategies for You, a time management consultancy.

"If anyone comments about how tired or distracted you seem, or notes a slippage in your attire, performance or output, you're overdoing the new business," Swedberg says. "If you are tardy or taking more sick days than usual or you feel more easily upset or frustrated at work, you are definitely at risk."

The best way to prevent this is to "completely compartmentalize" and refuse to shortchange your current employer, Swedberg says. Entrepreneurs should look to reframe both positions, and instead of thinking of a "full-time, bill-paying job," they should think of their day job as "what I do from 9 to 5." Instead of a "time- and money-sucking start-up," think of their venture as "what I do from 7 to 11 p.m. and Saturdays."

"This is a small mental shift, but it provides a huge release," she says. "There is no reason to jeopardize one for the other if you are willing to put in the hours at both."

Taking that strategy one step further, Swedberg says all entrepreneurs should have one full day per week that's a true break--no work at all.

"You will be amazed how many more ideas and energy you have for both," she says.

During this phase in the life of your business, it's important to focus on one task at a time, says Matt Julian, director of customer acquisition at BizFilings, a small-business incorporation provider.

"Focus on the task in front of you. By lending your focus to one challenge at a time, you'll generate better ideas -- whether for your current position or your start-up," Julian says, adding that savvy entrepreneurs understand that launching a company involves an enormous sacrifice of private time.

"It's a no-brainer that entrepreneurship requires personal sacrifice," he says. "To efficiently manage the effort required to start a business as well as your current job, be prepared to give up your personal time. Your hobbies or time spent with friends may be temporarily sidelined, but if you're willing to make some small tradeoffs in the beginning of your life as an entrepreneur, it proves you're passionate about your business idea and want to see it succeed."

For entrepreneurs who need a set schedule, Chuck Russell, senior partner with IT consulting firm Collective Intelligence, says it's a good idea to budget definite blocks of time for your small business.

"One of the things I tried to avoid was overcommitting given the relatively small number of hours I could spend on any project in a given week," Russell says of his own entrepreneurial experience. "So I began budgeting my time by allocating 20 to 28 hours per week to the new endeavor."

Once you feel your business is ready for a greater investment of your energy, it's definitely time to come clean to your employer about your new endeavor. If you're on good terms with your supervisors, Jeff Bell, professor of management at Dominican University in Chicago, says that it may be possible to "strike a deal" for part-time work.

"My recommendation would be to leave your full-time job but pursue independent contracting opportunities to provide supplemental income during the start-up phase," Bell says. "Folks can often strike this deal with their current employers who may understand the pursuit of a dream but may want to retain a needed skill set while they make succession plans for the entrepreneur's departure."

No matter what, do your best to keep a good relationship with your company, specifically any supervisors or colleagues you think are valuable for your network, says Sidnee Peck, director of entrepreneurial initiatives at the W.P. Carey School of Business.

"Be respectful and avoid the Jerry Maguire style of departure," Peck says. "No one knows if a business will be a success, and if you want to work in the industry again, you should not throw it in your company's face. At the same time, you do have to truly leave the company. That's the best way to be all in and devote yourself completely to your new business' success."