I can be described as a morning person, where waking up at 4:20 AM to catch a flight is no problem. My colleague on the other hand go to bed no earlier than midnight and often later than that.
We're both programmers, and if we're in a critical phase of a project, my colleague works until 3AM, and I start at 4AM. Still both times are in the middle of the night and we tend to get most work done at off working hours.
Question is why that is?