The period supposedly is 270 days now, according to this Hotmail Dev team "interview":

>> we have a policy of deleting emails after 270 days

http://www.reddit.com/r/IAmA/comments/ej32l/we_are_the_hotma... (do a search for "270" on the page to find the quote)

Although I have no idea when they changed it to 270 - it can't have been that long ago.