During the week, Tigerwulf sometimes hosts ARMA 3 missions. It would be best to monitor this ARMA forum for any announcements. There usually isn't too much advance notice sometimes.
On the weekend, we've been typically having some ARMA 3 play after our Iron Front Saturday event. Typically that means around a 5:30-6PM Eastern US start time. Check for announcements in this forum or pop in on Teamspeak around that time.