Understanding Clan Wars

So is there a specific time when Clan Wars takes place? And how many clan members have to be in the lobby for the win to count? I was helping a recruit on BO2 last night and didn't get to participate, but I'd really like to help out today! If anyone in the upper echelons of organization could get with me either here or on XBL and let me know where you'd like me to focus, I'd appreciate it. The game modes I play most are HC TDM and HC S&R. I play Core enough to not suck completely, so that's an option. Never played any of the new game modes, so I'd need to be teamed up with someone for instructional purposes.