@bortzmeyer It is already dubious, if it appears (and is authoritative there) in DNS, why it has to be in RDAP, as this seems to have more drawbacks (DNS and RDS have no reason to be publishing updates synchronously and at same frequency) than benefits. I doubt the TTL extension will be offered by lots of registries (probably none I would bet - there are already parts of secDNS extension about signature lifetimes NOT offered by any registry), so the point will be mostly solved that way.