I also run into that issue, Best workaround I've found is to open up the ATI control center and adjust that when it it gets to dark to see. You're looking for display color, under my digital flat panels, just adjust at night. I haven't tried but understand you can set it up to use a hot key for switching between your day and night settings.
I seriously hate the day-night cycle on MMO's. If you're looking for 'realism' You don't walk for 6 days and 5 nights in real life, why the ____ would you want to experience 5 nights in an hours play time??????. At least give the choice to turn it off for people who's idea of realism means a day/night cycle should have some relationship to wake/sleep cycles