I was thinking 9 months for some reason, but what do I know? ;-)
Believe me the crew will deteriorate long before that.
As other have noted, they will require special treatment and that means taking the rest of the crews resources.
That makes for an unhappy crew.
Yeah, the Babes get their own berthing an heads and an equal amount of guys get to sleep ontop of torpedoes and lose a shower and part the head?
Nope. I cant see it happening.