One thing that is important to clarify is that if you first immediately log onto the game and immediately enter the Role Select screen within a few seconds, the queue times will be inaccurate. This is because in the first 30 seconds after logging into the game, the client is pinging each of the different servers in order to find you the fastest servers to connect to. Until it knows which servers you will be connecting to, it can’t accurately estimate queue times.
That being said, queue times can be somewhat inaccurate for other reasons involving the matchmaker itself.