Badly timed earnings calls can be seriously bad news for executives and their company stock, according to a comprehensive study published in the Harvard Business Review.  

In an analysis of 26,500 earnings calls from 2001 to 2007, the researchers found that afternoon calls left executives sounding more “negative, irritable, and combative”, relative to calls held in the morning.

“Prior research has shown that physical and mental fatigue cause irritability and a decline in executive function, especially right before lunch and late in the afternoon,” summarized the researchers. “We theorized that a similar phenomenon might apply to earnings calls.”

The three university academics also found a correlation between cranky sounding executives and later stock performance, a correlation which is likely more troubling to CEOs.

They learned that “the tone of a call has real economic consequences – the more negative the tone, the more negative the returns over the five trading hours after the call.”

More dramatically, returns after negative calls drifted down for up to 15 days, and it could take 50 days before stock prices returned to normal.

“The increase in negative tone generated by moving a call from 8 AM to 3 PM translated to abnormal returns of -1.5 percent a year, on average,” said the researchers.

Management should listen more closely, and appreciate studies like this one, wrote the researchers: “Managers should consider these findings when scheduling calls…They should be aware that crankiness rises as the day wears on.”

Here’s the full study.