Happening the same way for me as well. Smooth for up to a minute then extreme lag, too much to handle. Previously great.
Windows 7 Pro
AMD Phenom II X4 960T 3 GHz
8GB Memory
AMD ATI 6870 Factory OC
DayZ installed on SSD OCZ Vertex 4
I thought it might have been the weather effect of all the rain-fall in the area but then I went inside buildings and noticed the lag occurring there as well.
Want steam name not computer name, must be that one of the devs wanted to derive the name from his own machines for convenience sake then forgot to change it back (commented out this line of code, uncommented my own dev-only line) :)
Speculation of course ;-)
Friend figured it out, not a bug. Even at this moment you can get on daytime servers. In the server browser click the time key to arrange the times of each server in order then find a range between 07:00 - 14:00 (sunrise between 6:30 - 7:00. When we were all wigging on the night time bug, I think the servers were updated, but maybe some config must have been switched back to default 24:00 time so all the servers started out with this config once patched - must be that they all get patched around the same exact time? Anyway, slowly but surely you began to see the server listings show a range of time.
I believe this is not determinable at this time on whether it's a bug or not, time-zone withstanding, joined several different daytime only servers and experienced night in all of them on US servers while it was still early/daytime in real life as well. What I don't know is if it does turn out to be a bug - is it server side or client side.
Also - can you please do your best to fix this before US eastern early evening tomorrow or no later than Friday? Reason is, today a friend and I gifted 3 games to our mates, plus 2-3 more bought the game just to join in. Then this night time only thing was their 1st impression of this game. They are ALL new to the game, none of them played the mod before. Please hurry I don't want to loose their interest before they even get started!
As a side note - I don't mind the dark, just consider adding additional types of light sources, example a lantern to put on a table inside a house or to carry that has a different kind of unfocused, circular light that lights up an area whereas the flashlight remains as it is... focused. Also consider items that can be powered by alternative power source such as solar power or hand cranking action LOL keep up the good work.