They might burn the midnight oil in a bid to get good grades, but students would be better off keeping regular bedtimes if they want to do well, a new study reveals.
Scientists found that irregular sleeping patterns were linked to poorer academic performance in college students putting their body clock off by up to three hours.
And they discovered that the timing of sleep is as important as number of hours slept.
The effects of variations in sleeping patterns is well documented but there has been little research into those who keep a regular bedtime.
In the new study from Brigham and Women's Hospital, researchers objectively measured sleep and circadian rhythms and the association to academic performance.
They found that irregular patterns of sleep and wakefulness correlated with lower grade point average, delayed sleep/wake timing, and delayed release of the sleep-promoting hormone melatonin.
The 61 full time students who took part were all undergraduates from Harvard College who kept a sleep diary for 30 days.
Researchers examined the relationship between the Sleep Regularity Index, sleep duration, distribution of sleep across the day, and academic performance during one term.
Lead author Dr Andrew Phillips, a biophysicist at the Division of Sleep and Circadian Disorders, Brigham and Women's Hospital, said: "Our results indicate that going to sleep and waking up at approximately the same time is as important as the number of hours one sleeps.
"Sleep regularity is a potentially important and modifiable factor independent from sleep duration.
"Using a mathematical model of the circadian clock, we were able to demonstrate that the difference in circadian timing between students with the most irregular sleep patterns and students with regular sleep patterns was consistent with their different patterns of daily light exposure.
"In particular, regular sleepers got significantly higher light levels during the daytime, and significantly lower light levels at night than irregular sleepers who slept more during daytime hours and less during nighttime hours."
Researchers found no significant difference in average sleep duration between most students with irregular sleep patterns and most regular sleepers.
By measuring the timing of melatonin release at sleep onset, the researchers were able to assess the timing of circadian rhythms.
On average, melatonin was released 2.6 hours later in students with the most irregular sleep patterns, compared to students with more regular sleep patterns.
Colleague in the research, Dr Charles Czeisler Director of the Sleep Health Institute, added: "We found that the body clock was shifted nearly three hours later in students with irregular schedules as compared to those who slept at more consistent times each night.
"For the students whose sleep and wake times were inconsistent, classes and exams that were scheduled for 9 a.m. were therefore occurring at 6am according to their body clock, at a time when performance is impaired.
"Ironically, they didn't save any time because in the end they slept just as much as those on a more regular schedule."
Researchers found that the circadian clock takes time to adjust to schedule changes, and is highly sensitive to patterns of light exposure.
Irregular sleepers, who frequently changed the pattern of when they slept and consequently their pattern of light-dark exposure, experienced misalignment between the circadian system and the sleep-wake cycle.
Researchers concluded that increased exposure to daytime light and less exposure to electronic light-emitting devices before bedtime, may be effective in improving sleep regularity.
The results were published in the journal Scientific Reports.