I would say SEO in an ongoing process. The time required to rank the website depends on:
Competition of the Keywords: For local keywords like SEO Company Delhi it might take 6 months for nationwide keywords like SEO Company India it might take 12 months. For local keywords you are only competing with local companies so the competition is less as compare to companies across India.
Present State of Website: What is the present ranking of the website? If the website is already ranking within the Top 50 results it would take less time to push the ranking within the Top 10 results as compared to if the website is not visible on search engines or ranking very low.
Competitors SEO Effort: What is the amount of effort the competitors have put in to the rank themselves? It is basically a comparison study or competitor analysis. The more effort they have put in to rank themselves the more time and effort it would take to bring them down.
Domain Age: How old is your Domain Name. New Domain names take a little longer than usual to rank on search engines. Google prefers websites which have been online for more than 2 years.
Number of Back Links: If you have some good back links already pointing to the website it would take less time to rank the website. If not then we would have to build links from scratch.
Pages Indexed: The more pages indexed the better it is as you can target more keywords on the website. More Pages also help to increase the density of the keywords on the website.
STT [SEO Takes Time]: Dont expect results from the first month itself. SEO Takes Time, you cant expect to be ranked ahead of the competition who have been working hard and regularly on the their websites in a couple of month. The day your effort is more than your competitors (Content and Backlinks) it is more likely that you would be placed ahead of them. Break down the effort over 6 – 12 months period depending on the competition of the keywords. Every month when you add pages / write articles and build links, search engines will crawl them and keep improving your ranking.
SEO is an On Going Process: Once the rankings are achieved you still need to keep working on the website so that you stay ahead of the competition otherwise your websites ranking would drop or the competitors would be ranked ahead of you.
DO NOT: Put all effort in 1 month as this might black list the website. Go slow and steady and see the results yourself.