I’ve been asked a few times about the real time versus in-game time. Like all things DayZ Mod, the documentation is hard to come by, but I think this is how it works. If you know of any other info, let me know.
The in-game time is based on a static start time of 16:00 (4pm) which is set at Server Restart. This means that conceptually, a server “day” goes from 4pm – 10pm and it will be daylight right after restart and darkness toward the end of the cycle.
Another option would be to let the server stay on the local time of the server, but that would mean that it would probably be dark from the 9pm ET restart to the 3am ET restart and then half of the next cycle.