It is indeed possible for some people to train themselves to get less sleep, reports Time magazine, even if it is not always advisable. 

Horne’s research shows that people can cut down their regular sleep to about six hours a night, plus a short nap during the day, as long as they do it gradually. In one study, he asked people who regularly slept seven to 8.5 hours a night to shorten their sleep by going to bed a certain amount of time later each night. Volunteers started by pushing back their bedtime one hour during the first week, and then pushed it back by 1.5 hours for the next three weeks. After doing this and waking up at the same time each morning, people were able to successfully function—and get high-quality sleep—on just six to 6.5 hours of sleep each night.

Gradually going to bed later might work well for some, but Horne says he wouldn’t recommend it for people who already feel like their sleep time is constricted. If you feel sleepy during the day, Horne said, then six hours is probably not enough for you. Instead, he says, focus on getting quality sleep rather than worrying about the quantity.