Honestly speaking; ‘it depends’. Search Engine algorithms are complex grading and evaluation systems and getting ranked higher in the Search Engine Results Page takes time depending on a lot of factors some of which include the type and quality of SEO that has been performed on your website, general structure of your webpage, domain rating, content quality, keyword selection etc.
A research by ‘Ahrefs’ concluded that the average minimum time required to rank in the first page of google is form 4-6 months. These figures are also supported by relaiblesoft.net and forbes.com. However, it is to be understood that these time durations do not mean that SEO will ensure results in 4-6 months rather it means that results will start appearing within this time duration. It will still take time to fully achieve the potential promised by SEO however the long-term benefits are worth the wait. Moreover, it is not a static effort rather a dynamic behavior i.e. your webpage would be constantly improving and with the right techniques this process can be accelerated as well.
Note: Agencies giving guarantee for seo or any marketing related services is all fake and you should avoid such agencies as results depend on scenario to scenario its also mentioned on google forums.