I would think that it could happen as late as June 7
That is impossible this cycle. Over half of all delegates available during the entire primary season will be awarded during the first two weeks of voting.
Unlikely at this point, perhaps, but not impossible if the race is close. If Sanders wins Iowa and NH, it could tighten up, but if Clinton were to win Iowa, she may become unstopable.
I love that many Bernie fans think he is going to be the 2nd coming of Obama 08. Sorry guys, it ain't happening.
Not all Sanders supports are not predicting that he will win, but Clinton hasn't won this thing yet.
Before February it is too soon to predict how long this thing will go on. If Clinton does win the nomination
it is entirely possible that Trump will win the Republican nomination sooner.