I could see that after doing SEO for certain keyphrases, the search engine ranks them well (in top 10) only after 40 to 60 days.
Now say I have a key phrase "xyz". Now is it a good approach to do link building and other SEO stuff till it gets ranked well (40 to 60 days). A more smarter approach would be to limit the SEO work and move on to next key phrase without waiting on the same keyprase.
Is there some limit where I can draw a limit on the number of back links and other SEO stuff for a particular key phrase ?
Sounds like you are more a linking strategist positioning webpages for long tail search engine result pages (SERP) contests moreso than someone actually skilled in SEO. I know that sounds mean but to think that your web pages will automatically appear in the the first page for anything competitive in 40-60 days indicates to me that you are on the wrong track as to what constitutes a meaningful niche SERP market.