The 24hr clock system used in the trainz games controls the time of when certain assets with in-built lighting scripts - such as street lights, internal building lights, and locomotives with night-mode - switches on and off. TS12 for example, all in-game asset lights usually switch on at the game clock time 6:00pm (18:00) and off again at 6:00am, about an hour before and after the position of where the sun is in relation to just above the horizon.
Andy.