You can change the day/night cycle easily with a console command. Thereby is no need to start a new game. Open console and type the following commands:

twoworldscheats 1
ec.setdaylength 3600 70 205 (but i'm using ec.setdaylength 10800 80 205)

3600 = daylength in seconds // 3600 = 60 minutes = 1 hour
70 (index 0...205) = sunrising
205 (index 0...205) = moonrising

Have a nice play, thanks for solution to Miho from insidetwoworlds.com.