How does the day/night cycle work?

There are badass ranks for killing enemies both at night and during the day.Time also seems to progress while fast traveling. How is the amount of time determined? How long is one in game day/night?

Solution 1:

The day/night cycle completes every 24 minutes.

By observing the clock in Lynchwood, you'll note that, after 12:59 on the clock, it goes to 1:00, thus indicating that it's essentially a 12-hour in-game clock. You'll also see that the day/night cycle in the sky corresponds to what we typically expect as the "hours" pass.

In addition, for every second that passes out of the game, the minute ticks once on the clock. This tells us:

• 1 second = 1 minute in-game
• 1 minute = 1 hour in-game
• 24 minutes = 24 hours (1 day) in-game

Solution 2:

Get in a vehicle. Drive. When the headlights turn on, it's night.

Alternatively, go to the Friendship Gulag and kill some robots. When the searchlights turn on, it's night.