An ‘Owl’ is someone whose body clock is set to sleep later than average, and a ‘Lark’ is someone whose set to sleep earlier than average. It is your inherent melatonin rhythm and temperature rhythm that determine when you sleep.
Being an Owl or Lark can impact how well you do with different schedules. Generally speaking, Owls do better with later schedules and shift work like graveyard. Larks are the ones you’d want to open the shop in the morning. It’s important to know that alertness fluctuates over the 24 hours in almost the same curve as temperature. As your temperature drops you are less alert and more sleepy. If you get into bed and try to sleep before your body is ready, you may experience this as insomnia. About 10% of chronic insomniacs actually are Owls, and if they go to bed later have no problem sleeping.
To determine if you are an Owl or Lark you can do the Horne-Ostberg Morningness-Eveningness questionnaire, which was developed in 1976. You can find a modified version of it online at http://web.ukonline.co.uk/bjlogie/test.htm.
This information can help you develop a lifestyle that best suits your circadian rhythm. If you are not able to shift the time of your commitments, a sleep specialist may be able to help shift your circadian rhythm.