TTFB Not Used in Search Ranking
Speed is an important aspect of the website experience but there are some aspects that may not matter as many of search engine optimization (SEO) professionals have been led to believe.
Google's John Mueller replied to a question recently on Twitter about whether SEOs should be concerned about "time-to-first-byte" or TTFB or if focusing on speeding up page load speed through code improvements, image optimization, etc., suffices.
Mueller responded that Google does not, as far as he knows, use TTFB for search, but suggested that it can be a good proxy for user-facing speed.
Speed is obviously important to the user experience but what Mueller is suggesting is that it is probably best not to just blindly focus on it if the aim is to see improvements in search ranking/optimization.
Many websites today take advantage of content delivery networks to improve their page speed (along with numerous other best practices) but the benefit of their use may really come well after the first byte has been delivered.