But the night hours of the American timezones is always a good starting point. Weekends are also good. It varies but there are at times good nights where you can get a sizeable group of coop players.
As for what is being played, mostly the same maps as before. You can however go to the GoS site, click on Games, select Co-op in the Scoring dropdown, and click Filter. It will show you a list of co-op maps played on the server. You can even search for a specific map to see when or if it has even been played on the server.
