Adam Seligman, a South Florida transactional lawyer, saw a potential client hire someone else when Seligman took 45 minutes to respond.

Seligman has no trouble serving clients across time zones, from Malaysia to Israel, but his experience with this client illustrates how fast business moves and how lawyers struggle to keep up. "If i don't call someone back quick enough," he said, "It's a missed opportunity. It's a missed deal."

The challenge goes beyond losing business. Some lawyers are concerned the demands for speed make it harder to give clients need well-reasoned advice.

"The lack of time to just sit and think about something is difficult," said Mike Voynich, an Eversheds Sutherland partner in Atlanta who helps companies raise capital through private equity transactions.

Speed "forces us to be efficient," and that's a good thing, he allowed. But, "the faster the turnaround, the less effective we are."

Voynich wants to "toil with the case law" underlying the deal documents, and he wants associates to wrestle with the issues so they understand why deals are structured the way they are.

Voynich's concerns reflect a practice-level aspect to a mental health risk identified by Patrick Krill, a lawyer and mental health counselor. He wrote that when clients tell their lawyer, "'Just make it happen,' it would seem, in a sense, like they are simply signaling their confidence and bestowing their praise. In reality, the timeline may be disastrously unreasonable, the expectations inhumane, and the assignment itself utterly unclear but, damn it, they know you'll come through."

An informal survey of lawyers in markets such as New York, Philadelphia, New Jersey, Atlanta and South Florida, revealed a common approach to this challenge: Manage client expectations.

Susan Eisenberg, the Miami managing partner of Cozen O'Connor, said, "I think the need for speed has definitely increased over time and obviously because of technology. I think the expectation of clients now is that they want responses immediately, and it doesn't matter what time of the day or night they're reaching out."

But if the matter is absolutely something you can't review, a lawyer has to say, "I need some time," she said.

Kevin Kent, a litigation partner at Conrad O'Brien in Philadelphia, said, "There are times when you have to say, 'I can't give you an answer, even a preliminary one, because it would require too much speculation, and I don't want to give you an answer that sends you in one direction and then has you do a 180 in a few days.'"

"In my experience, clients respect a response that's very blunt, where you say, 'I really do have to take a meaningful look at this because I can't give you a preliminary answer that's acceptable.'"

Doug Sandberg, the general counsel at First View Financial and former general counsel at Worldpay US in Atlanta, said managing internal clients' expectations is critical to ensuring lawyers have enough time to get to the right answer.

"I'd prefer a right answer to a fast answer," he said.

Paul Marino, managing partner of Day Pitney's New Jersey office, said speed is "a differentiating factor for clients. They really want to know they can reach you."

At his firm, "it's addressed with our attorneys in general, that we expect [them] to be extremely responsive," Marino said. "But you've got to be responsive without being irresponsible."

Expectations depend on the client and the type of case. And demanding immediate assistance can be reasonable in certain contexts, he said, such as in a situation where a court issues an order to show cause.

Vito A. Gagliardi Jr., managing principal Porzio, Bromberg & Newman in New Jersey, said that what's reasonable is largely subjective. When it comes to email, "my sense of what's important is less relevant than the sender's sense of what's important," he said.

"If you're measuring reasonableness by what the marketplace expects," then a high level of responsiveness is reasonable, Gagliardi said.

Responding to a client's email at 10:30 p.m. on a Thursday, or at 1 p.m. on a Sunday?

"At this point," he said, "clients expect that."

Henry Morgenbesser, a name partner at Katzke & Morgenbesser in New York, said, "I think the practice of the law itself, whether you are at a big firm or small firm, has become more demanding. We're in an instant-gratification society. I think technology has increased that expectation."

"My wife tells me I hunch over a computer all day, and the first thing I do when I come home is hunch over it on my kitchen table,' he said.

But Morgenbesser is keenly aware that now that he has his own practice he has more control over when and where he works. Morgenbesser's partner, Michael Katzke, as a matter of fact, turned away a promising new client in favor of watching his son play lacrosse. The CEO called him on a Friday and wanted the work done by Sunday.

David Gialanella, Zack Needles, Susan DeSantis and Cathy Wilson contributed to this report.