First of all welcome in our community forum
No it is not necessary actually there is no actual time frame for time stuffing on any keywords.
Haha No @RC-Fitness-Wear that is not the only reason actually, Google needs time to propagate your web results in search engine.
Even today I remember that time when I was publish an anarticle and that rank in Google #1 Page just in 5 minutes
Without putting your attention on backlinks give your precious time to content marketing
Yes you can do SEO as many keywords you like. Right now KnowledgeIDea have more than 3k keywords where we did SEO It's fair to do
Thanks for your taking interest with us!