The biological clock is the sequence of behavioral changes every 24 hours. It can be altered, but it takes a while for the body to become accustomed to it. There are high points and low points in a biological clock. The high point is usually from 3pm to 5pm, while the low point is from 3am to 5am, although they might vary. Behavior is influenced by biological clocks in the way you function throughout the day, whether it be perky and energetic during your high point, or gloomy and tired during your low point.