I hear a lot of confusion when people talk about joining a DayZ server in daytime. I’m personally not a big fan of playing at night in the dark without a set of NVGs.
Here is a quick video explaining how to find a daytime server.
Quite simply, all you have to do is filter the “time” column. The times displayed are in 24-hour format. The best time to join is 8:00 when the sun is just coming up and up until about 15:00 (3 PM) which gives you some time to play before it gets dark (about 17:00 or 5 pm).