Right now, it takes up to 40+ minutes just to get into any MvM game. Not to mention I don't have 5 friends willing to play this at the same time, so playing this mode is probably improbable right now. Even with the join game in progress checked, it's still not letting me in. Released on the first day and it's already failing. What's worse is that you have to buy tickets to use just to get anything noteworthy of your success. Valve sure know how to disappoint.
By the way, if you're having trouble getting to download in the first place, just change your downloading region to another country. It'll go by a lot faster.