It's one of the cardinal rules on Shark Tank: never appear on the show unless you are fully committed to your company. 

But on Friday's episode of Shark Tank, Mark Cuban ignored the concerns of his fellow sharks and offered part-time entrepreneur Shaan Patel, the founder of test prep company 2400 Expert, $250,000 for a 20 percent stake in his company. 

It's not that Patel, 26, isn't committed to 2400 Expert, which is based in Las Vegas. He just doesn't have a lot of spare time to commit. In addition to being the CEO of 2400 Expert, Patel is a medical student at the University of Southern California and is pursuing his MBA at Yale University. 

The Sharks were impressed by Patel's credentials: He earned a perfect score on the SAT and helped 2400 Expert generate $1.2 million in sales in four years. But they were taken aback when they found out what else he had on his plate.

"You can't be a part-time entrepreneur," Kevin O'Leary insisted. 

But Patel's ambition was enough to persuade Cuban that he was an entrepreneur worth investing in. 

"One of the beautiful things about Shark Tank... is that you get to 'acquihire' all the time," said Cuban. "More often than not, you're betting on the brains behind the company." He then asked Patel to promise him that no matter how many other careers he decided to pursue, that 2400 Expert would "always be part of the ride," before making a deal. 

"Of course, this company is my baby," Patel replied.

In an interview with Inc., Patel insisted his ambitions aren't as unrealistic as they may seem.

"I have grown this company from zero dollars to $1.2 million in sales prior to Shark Tank,  while I was in medical school, during some of the hardest years," Patel says. "I tried to convey that to [the sharks], that I had a proven track record going in."

Cuban reiterated his support for Patel in an email to Inc.

"I think trying to make America's kids smarter is a good thing, and Shaan and his company are perfectly positioned to accomplish that," he said. 

Patel will soon be able to devote a little bit more time to 2400 Expert. He is in his last semester of business school and then will have one more year of medical school. He took off two years between his third and fourth year of medical school to complete his MBA, a move he says is not all that uncommon. Many other medical students do the same to pursue another advanced degree or work in a research lab.  

"I've always been an entrepreneur. School has always been really important to me, but I've always needed to have something on the side" Patel said. 

Patel's dream, he says, would be to work as a doctor three days a week and then devote the rest of his time to 2400 Expert.

Patel says that his deal with Cuban officially closed a few weeks ago, and he is focused on expanding 2400 Expert's services to six more cities. 2400 Expert offers both online and in-person courses that help students develop better studying habits to prepare for the SAT and other standardized tests. The courses last six weeks and typically cost around $999 and $599 for a in-person and online course, respectively. 

Even as his commitments grow, Patel says he takes a simple approach to managing his busy schedule: Make a to-do list every night. 

"I just try as much as I can to focus on the next day's task and what's important, and that prevents me from getting overwhelmed," Patel says.