Originally posted by Shillen
The 3 turn grace period on culture flipping is a myth. Or maybe it was the case in vanilla I don't know. But I've had cities flip in 2 turns several times in both GOTM and non-GOTM games. I haven't had it happen in 1-turn yet so I don't know if that's possible or not.
Based on my experience of having to spend countless hours on Civ3, the Culture Flipping really come down to this:
There are actually two different types of Culture Flip:
Type I:
It flips because of the Culture Squeeze. In this case, the Culture of the near by cities are too strong; therefore, it causes your city to flip. I'm sure everyone has known the tips and tricks for this one; therefore, there is no need for me to explain it any further.
Type II:
Whenever there is Civil Disorder somewhere in your kingdom, there will be an immediate chance that one of your cities will flip. Here is an example: Let's say you reduce your enemy to only 1 city and and he is in some remote island far far away from your nearest cities. His border isn't touching your border in anyway; however, suddenly, one of your cities flip back to him. Why? If you squeeze out the rebellion from your recently captured city too quickly, that city may fall into Civil Disorder for 1 turn before you can starve its citizens; therefore, an immediate chance for your weakest cities to flip.
Therefore, sometimes it may be a good idea not to squeeze out the rebels right away. I usually ignore the rebels and go ahead to eliminate their former ruler first then come back to deal with the rest of the rebels later.

If I need to deal with the rebels right away, I would make sure that I have plenty of troops to prevent the Culture Flip and I also make sure that I move all of my troop out of my other cities just in case. Basically, just as long as none of the cities under your control fall into Civil Disorders, your 3 turn grace period will be safe.
