According to me you can get ranked in 3months if completion is medium but if the compettion is high then it can take update 6-8 months

i would say between half a year up to a year will be a good guess. depends on the comp and your own doing - content and back linking plan. try to look for used domain or a site for sale. will be faster than building new website from scratch.

In google one month or less for low competitive keyword,1-3 months for medium competitive keyword and 3-6 month for high competitive keyword,

I Think SEO is about Two Aspect. Effort and Luck. I dont know about exact time