FYI for midnight launch you can change your clock and still do it ONLINE for the datestamp. Just change your timezone to one that's about to strike midnight so you can stay on live and put a timestamp on the achievement.
400,000gs reached 1-13-15. Used D4 to get it (get it, it has 4 in the name) due to my disgust with how Halo: MCC has been handled. Achievement used for 400k milestone: Business as Usual.