I operate authoritative name servers for almost 10.000 domains. Originally, I used a default TTL of 2 days, as recommended by RIPE-203¹ (which is also compatible with the recommendations of RFC 1912²), but this was not accepted by users, who didn’t want to wait two days. Therefore, for all records except SOA and NS records, I changed the default TTL to one hour, which I still use as the default value unless a change is scheduled and/or planned, in which case I lower it to 5 minutes. I do not want to lower it any more, as I’ve heard rumors of buggy resolvers interpreting “too low” TTLs as bad, and reverting to some very-high default TTL, and thereby wrecking my carefully planned DNS changeover. I have, however, not seen any real numbers or good references on what numbers are “too low”, and would like to hear from anyone who might have some information on this.