Just guessing here, but trying to look ahead...
Thus far, one new 'girlfriend' has been added roughly every week. (at the weekend).
Add Sarah this coming Friday.
Misaki, Alison, Catherine, and Hannah have all had enough progress they could all be in the next 2 or, more likely, 3 weeks. (with Catherine and Hannah being a double).
Rachel, and Elizabeth seem like they're also probably in the production line somewhere, so add another 1/2 weeks there...
So I'd put it as a minimum of 23-25 days to go (so call it 50 days total), more likely 37-39 (65 total).
The FF storyline will also require a decent amount of time to play out, but lets say it works within the girl's timeframe...maybe add a few more days to get to the next Tuesday council meeting, depending on how it's going to be wrapped up.
In real terms though, well....We're talking quite a few years, most likely around a decade given the current pace of updates.