There is no upper limit to building local citations and it don’t need to be done only one time. You can create as many citatons as you wish provided they are unique and high quality, related to your niche and have consistent NAP information for Local SEO. Other factors that influence the number of citations are the geographical location, the size of your city.
Citations provide the much needed geographical relevancy to your business. Sometimes building citations on low quality directory listings can do more harm than good in search engines so bear that in mind.