@Darielle I wouldn't say you have too many factories, I see that many on lots of towns. As someone who generally only logs in twice a day that chapter took forever, I forgot precisely how long but best guess would be say 8-9months for ch 17 and again for 18. The game isn't designed for a casual player in the later chapters, it gets harder and harder.
The numbers I hear from people on those later chapters is closer to 6 months than 3 months. Previously 3months was pretty standard, portal profits of course sped this up for earlier chapters.