It is the same with rain and fog, if you join later, or he joins later, the time of day on the server might have been changed.
Yesterday it was night for the majority of us, but for some it was daytime (we actually talked about that on teamspeak as well )
You (or somebody of your clan mates) actually told me about it ingame yesterday. But that would make any sence if me or Gravoth would actually 'join later', but we both were playing without of disconnects/leaving the server. I've started to spectate him for a reason, not in all of a sudden. He had 4 or 5 consecutive maps in a row in a daylight, which were night maps in actual game. I've screened only 2 of them because I've actually played other 2 or 3 maps and didn't have time to screen his gameplay. Anyways nobody seem to bother about that, so I think that this is probably not considered as a cheat or something. Just a funny fact. And that story about when it was a night time for the most part of you, but for some ('smart' ones) it was daytime, makes it actually even funnier