Can you build a house slowly or does the city give you timeline you have to follow?

iam not sure it better you ask your location office and ask them that. you might not get the right answer from here. 

I just bought a single bag of concrete yesterday to start pouring the foundation sooo...

I'm sure the city trusts that someone building a house does not want to waste their own money or have to do something twice, because that's what someone not doing it in a timely manner would be doing. 

Ask the city's zoning and planning office.

I dont think there is a Time Limit as to how fast the House has to be Built it Probably does have some Guidelines tho for those you have to Contact the City 

That can depend on where you live. Also there are certain steps that you can't delay or the house will start to deteriorate. As an example: Once you have the framing done you can't wait too long or the wood will start to warp, twist and even begin to rot depending on how long you wait to dry in the house.