Googles John Mueller stated on Reddit that if you desire to slow Google from crawling your site (or speed it up), it can take about a day from when you set the crawl rate setting in Google Search Console for it to kick in. The official documentation kind if implies it takes two to 3 days.John stated in the thread “Set the crawl rate down in search console. Even the “Immediate relief” choices can take a day for Google to select up on and adapt.In any occasion, keep in mind, the fastest option is probably to increase your server capacity and resources or block Googlebot, but nearly no one desires to obstruct Googlebot.You can discover more about the crawl rate feature in the assistance documents.Forum discussion at Reddit.