Clock Skew Trap: Why R2 Presigned URLs Expire Before Their TTL

Clock skew between distributed infrastructure causes R2 presigned URLs to expire earlier than their nominal TTL, often appearing as mysterious permission errors to end users. This problem is particularly acute for mobile clients and carrier proxies—especially those in Asia and Korea—where aggressive TTL handling can reject valid URLs prematurely. Implementing a signing buffer provides a practical, production-tested solution that eliminates these timing issues without requiring complex clock synchronization.