Shutterstock Our body goes into a naturally drowsy slump every day, usually around 2 or 3 p.m. One way to stay alert during this slump is to take a 10 to 20 minute nap. Some studies suggest sipping a coffee beforehand can make your afternoon nap even better. It typically takes around 25 minutes for the effects of a coffee to completely kick in, so you'll wake up alert, chipper and ready to focus. Something pretty crazy happens in your body at about 2 or 3 p.m.