I haven't been playing for very long and I know it was daylight at one point, now I feel like night is taking forever! I can't tell if the sun cycle happened because I moved around or if it is just on a clock cycle. If it's time based, how long does it take? If it's event based, which areas trigger the change?
the progression between day and night is time based, so 5 Minutes in realtime match 1 hour Ingame-Risen Time.
But i think that your day-night cycle is corrupt! Its a well known Bug taking place on AMD Dual Core PCs. A Solution is to get the latest AMD Dual Core Optimizer. Hope that works for you: AMD Optimizer
As the other answer mentions, the risen day-night cycle is based on time.
There are a few options to fast-forward time (and one to slow it down) though:
Note that I haven't actually played around with the console that much, and I haven't experimented with
See also the "Time" entry in the Risen Wikia's FAQ: http://risen.wikia.com/wiki/Risen_FAQ#Time