Politician Archive

I am wondering how long it takes for the player city to actually get to rank 4. I have place mine and we are starting to get residence. We want to know how long it will be to actually get the shuttle port since we r in the middle of no where literally right now. I have it is 4 weeks, but i also heard city grows once every week if you have enough residences. I came up with this formula and I wanted to see if this really says it will be three weeks and contradicts the 4 week theory. here it is :

Week 1 (placement of city hall) = Rank 1
Week 2 (seven days from placement) = Rank 2
Week 3 (fourteen days from placement)= Rank 3
Week 4 (twenty - one days from placement)= Rank 4

Based on this it takes 21 days or 3 weeks to reach the Rank 4 mark. Please someone help me here.