How long do you think it takes for Google to start ranking and taking your new website serious. How many backlinks, and months or years before your site starts hitting the top pages for very competetive keywords? L
It is not something that is measurable. It would vary a lot depending on multiple factors. For one keyword you might be able to dominate in a month with very few backlinks. For another keyword it might take hundreds of links and 6+ months. It depends on things like your onpage seo, the quality of your links, your link anchor text, the age of your domain, etc. The length of time can vary a lot depending on how quickly you acquire links too. So nobody can give you a definite answer.
Its not really measurable it mostly trial and error but in very general terms - the more the competition the harder it gets to RANK - the more backlinks you get the easier it gets to RANK - the more relevant the links the easier it gets to RANK - the longer your site exists (domain age) the easier it gets to RANK - the more you update it with unique content the easier it gets to RANK etc