It takes about 15 to 30 minutes for you to feel the effect of the caffeine, and the benefit will last for three to four hours, Rosekind says. “If you plan strategically to use the caffeine every few hours, you can keep yourself at a pretty good level of performance,” he says.
The best strategy: Have your caffeine and lie down for a 30-minute nap. You’ll wake up feeling refreshed, he says.
One caveat: When you finally stop drinking your caffeinated beverage, expect a crash. “The caffeine masks the sleepiness, [but] the sleepiness just keeps building up,” Rosekind says.