Redirect latency is the time between a user clicking a shortened URL and the destination page beginning to load. This delay directly impacts user experience; Google's research shows that every additional 100 milliseconds of page load time reduces conversions by roughly 1%.
The total latency is the sum of several steps: DNS resolution (looking up the short URL domain, 20-120 ms), TCP connection (establishing a connection to the server, 10-50 ms), TLS handshake (setting up HTTPS encryption, 30-100 ms), server processing (fetching the redirect target from the database, 1-50 ms), and response transmission (returning the 301/302 response, 5-20 ms). A typical total falls between 70 and 340 ms.
Major URL shortening services optimize redirect latency to 50-100 ms through CDN edge caching. If you build your own service, an in-memory cache like Redis can bring server processing below 1 ms.
Redirect chains - multiple sequential redirects - multiply latency. A chain of short URL to another short URL to the final page doubles the delay. Google recommends avoiding redirect chains, and from an SEO perspective a single direct redirect is always preferable.
You can measure redirect latency with curl's -w option (which prints timing for each phase), Chrome DevTools' Network tab (which shows detailed redirect timing), or WebPageTest (a third-party performance tool). You can find related books on Amazon.