When is the best time to list in Boston?

I wanted to pose a question to everyone.  Conventional wisdom for rentals in Boston has always said that a September move in date is king for rentals but over the last few years I have begun to question that some.  Obviously for the student market there can be no question but I feel that for higher end units especially in the Back Bay/South End a June listing date is best.  There are a couple reasons for this,

First off, the hospitals in the area run on a June-June cycle.

Second, the South End and Back Bay are so nice in the summer that renting a nice unit in those areas in June is like falling off a log

Third, if the market is flooded around 9/1, any unit that comes to market before that will get much greater exposure because there are less listings to compete with.

Please, if anyone has any input on this I would love to hear it.