That'd be more difficult to do for the free version than we like. Currently, Joomla only tracks the initial registration date, which makes it very easy to force a new password on the first login. Unfortunately, there's nothing to track when passwords were updated, so we'd have to create a table, hook into the user component, and track when passwords were changed. It's a bit of work, and something we won't be taking on anytime soon.
Definitely appreciate the feedback, and hope this does at least a little of what you're looking for!
Timed password change
