[vavrusa]

Yes, there's a cap on both negative and positive cache lifetime. The reason is reducing the blast radius as accidents happen, and it hurts especially on long infrastructure records (mistake during repointing NSs, bad glue, expired DS etc.) We're going to be looking into making the cap more dynamic over time.

[LinuxBender]

I do this at home as well, using Unbound DNS to set a min and max TTL. It's taboo on public DNS recursors, but totally makes sense. Some folks try to use DNS as real time load balancers and will set crazy low TTL's like 1 second or even 0 (which violates RFC's)