When the clock moves ahead one hour each spring for Daylight Saving Time, we’re all robbed of some sleep. For night owls, the effect can be especially disruptive.

Early risers tend to bounce back from the time change in a few days. But new findings by University of Michigan scientists show that the late-night crowd may need a week or more to rebalance their sleep schedule.

To establish their findings, they tracked the sleep habits of more than 800 physicians in their first year of training after medical school. Using a large data set from the United Kingdom, they also distilled the genetic factors that predispose someone to being an early bird or a night owl.

From there, the researchers focused on two groups of about 130 physicians each. They were the ones who had the strongest “early bird” and “night owl” tendencies.

After the Daylight Saving Time change, the early risers had adjusted their sleep times by the following Tuesday. The late-night group struggled considerably more, needing at least until the next Saturday to regroup.

No such differences were seen between the two groups during the fall, when clocks roll back one hour.

Some of Daylight Saving Time’s effects were already known, such as its influence on vehicle crashes and heart attacks. The latest findings shed new light on how genes and the environment can affect people with different rhythms to their biological clocks. The researchers say it’s another reason to consider abolishing Daylight Saving Time.

And while the spring time change can make night owls sluggish, it also provides some answers — and an excuse to sleep in for at least a week.