Do you believe that the earlier you go to bed and the earlier you get up, the healthier, happier, and more productive you’ll be? Many people do, and many websites, including this one, offer lots of advice about how to be a morning person and why it’s so important to be one.

Well, maybe it isn’t so important after all. A new study from Harvard traced the sleep habits of 61 students over 30 days and correlated those habits with the students’ grades. It found that students who got regular sleep–that is, who went to bed and woke up about the same time every day–did better in school than those who slept irregular hours. You might expect that much to be true, but here are some more surprising findings:

1. You don’t have to wake up at 5 a.m. after all.

The study did find that students were better off if they slept during “nighttime” hours, but it defined those hours as 10 pm to 10 am. As Charles Czeisler, M.D., chief of the Sleep and Circadian Disorders Division at Brigham and Women’s Hospital told CNN, “The results of this study are not suggesting everybody has to be a goody-two-shoes. So if you go to bed at 2 and get up at 9, that’s fine. You just have to consistently do the same thing.”

2. Getting enough sleep won’t help you if you sleep irregular hours.

The researchers expected to find that the irregular sleepers who stayed up till all hours were sleeping fewer hours than their regular-sleeping counterparts. But no–both groups were sleeping about the same number of hours in total because the irregular sleepers were napping during the day. Their grades still suffered, proving what most of know by instinct: A nap can be nice but it’s no replacement for a good night’s sleep.

3. Sleeping irregular hours can make you fat.

Irregular sleepers had delayed circadian rhythms compared to regular sleepers. Both phenomena have been shown to be related to weight gain in earlier studies, the researchers note. If that information isn’t enough to make you stop pulling all-nighters, I don’t know what is.

4. Irregular sleep could be a symptom of something else.

One thing the study didn’t do is measure the things that might cause someone to become an irregular sleeper, and how they might affect academic performance. For example, if you’re someone who goes to bed at precisely 10 pm every night and wakes up at precisely 5 am every morning, chances are you’re a highly disciplined sort, which means you might also have the discipline to get all your homework done early. Conversely, irregular sleep can be a symptom of depression, and depression could certainly affect one’s academic performance.