I've been told that asymmetric matchmaking kicks in after a ticket has been active for 30 seconds. This is far too brief, and it's causing very large match quality issues. We have fairly high playercount matches, and one player in an underpopulated region can apparently cause thirty other players to match with into the wrong region because their own region rule has expanded much further than the other players'.
I have an example match where one player posted extremely high pings to all regions except Japan, and was matching for about two minutes. The RegionPreferences ended up placing the match in Japan, but it matched it up with mostly non-Japanese players who had been matching for 10-20 seconds at most. We don't view this as being desireable; from the perspective of most players other than the sole player in Japan, this was a bad match.