Depends on the day of the week and time of day, or if there is a popular event like Trials. I've had random times where MM seems to take forever, but that's usually only a game or two and then it seems to pickup. I think some of it has to do with their system of trying to match you with similarly skilled players. I've noticed my extended MM taking times seem to take play on my first two games of the day and then the algorithm seems to figure out where to stick me. There have been days when I've been on a hot streak and really playing well so I'll randomly get a long MM midday, or the reverse, I've bombed a lot of matches and I'll get a long one.