When should I start monitoring SEO during a website launch?

Start before launch by recording a baseline for search traffic, leads or sales, rankings, indexed pages, and important URLs. Immediately after launch, confirm that analytics works, old URLs reach the right new pages, priority pages load correctly, and Search Console's Page indexing and URL Inspection reports show no unexpected problems. Use Crawl stats when you need to understand how Google is accessing the site. Keep reviewing traffic, results, rankings, and indexing for several weeks because some changes appear only after search engines revisit the new site.