found the post where the rating system for the realtime ladder was officially described:https://www.warlight.net/blog/index.php/2014/03/website-update-2-5-real-time-ladder/
Edited 4/14/2015 13:07:31
Ratings for the real-time ladder are calculated in a completely different manner than the other three ladders. The real-time ladder uses the TrueSkill algorithm to determine player’s ratings.
Unlike the other ladders, ratings will update immediately after a game finishes. After every game, you can refresh your ladder page to see your new rating.
This makes the rating method much simpler than the other ladders. The ripple effect of the other ladders is not present — the rating change is affected only by the rating of your opponent when you played, not their future changes. Also, games never expire like they do in the other ladders, but the TrueSkill algorithm weights newer games more highly, so you still have the ability to move your rating over time.
It takes around 15 completed games to receive a rank. Unlike the other ladders, you get a rank even while you’re not joined to the ladder. If you don’t play a real-time ladder game for 3 days, you’ll lose your rank and revert to “Not Ranked” until you play a game again. This doesn’t affect your rating.
Also unlike the other ladders, the real-time ladder does not award points for ranks. Instead, each win gives 4x the points that the equivalent game would give if you just created it on its own.