Humana is among the companies reporting its quarterly numbers on Wednesday as earnings season continues. The health insurance giant always releases its earnings before the markets open. Whole Foods reports the same day, but the grocery chain always waits until after the closing bell.

If you’ve ever wondered why companies go one way or the other, it’s worth noting the Securities and Exchange Commission doesn’t care what time of day companies report their quarterly earnings.

So it comes down to factors like: what’s the best time to put the CEO on the phone with investors and analysts?  

“Some people are morning people and some people are afternoon people,” says Jeff Morgan, president of the National Investor Relations Institute. He adds that once a company picks a time, it sticks. “We want to be sure that whatever we do every quarter, we do the same thing the next quarter, so that there’s not anybody wondering why we’re making changes.”

A recent study found that 66 percent of companies hold earnings calls at the same time every quarter. Co-author Elizabeth Demers, an associate professor of accounting at the University of Virginia’s Darden School of Business, says executives should avoid afternoon calls, when they might be hungry and cranky.

“What we find is that as the tone of the calls becomes more negative, the share price returns are also more negative,” Demers says. “In other words, the stock price responds to the negativity that’s being emitted on the calls.” 

Demers says size matters, too; a lot of small companies reporting earnings have to take whatever slot they can get.