A 'Dangerous Time' to drive is between midnight and 4am. Statistically, this is the most dangerous time of day to drive – there are more fatigued drivers on the road at this time, as well as more impaired drivers than normal.
On an individual Trip, "Dangerous Time" indicates the number of minutes of the trip that took place during this timeframe.
"Dangerous Time" is also a factor in your overall score, and the Dangerous Time score is based on the degree to which you drive during this time period. A higher score means less driving at dangerous times, so aim for 100!