I've always thought FF1 would take about a year (maybe a year and a half) due to all the traveling involved. The others I'm not really sure about.

7 and 8 would probably take a long time (about a year or so) because of these games' complex plots.

9... I'm pretty sure this would be pretty quick. In fact, I did some digging and found a site dedicated to Beatrix that gives a timeline detailing all the events involving her. Based on that, it would take about three or four months. Here's the link in case anyone wants to take a look. It's not very good English, but you can understand the basic idea of what it says.