When will I get to be Thanos? This random choosing system sucks
Edit: Guess what just happened? I finally got a power stone (first stone) dropped right in front of me and just as I was about to become Thanos another f**king dude came in to disrupt my capturing of the Stone and he got to be Thanos instead. :)
Try grabbing the first gem - it appears when the countdown is at 3:00 and drops near the edge of the circle on the Chitauri side.