Coffee has no effect on people who stay up late.

Researchers at Stanford University surveyed 50 college students about their caffeine intake and found a link between caffeine intake and "time type" (the time of day when people are most alert or active). Caffeine only affects the sleep of lark people who are used to going to bed early and getting up early, but does not interfere with the sleep of night owls who like to stay up late. For lark people, the more caffeine they consume, the longer they will wake up during sleep at night. This is not reflected in the "night owl" type.

The researchers warn that everyone's metabolism of caffeine is different. Some people can metabolize caffeine in a few hours, and some people drink coffee at noon and still have caffeine in the evening. If you are a lark, it is best not to eat too much caffeinated drinks such as coffee or tea after noon.