[jon-wood]

> Delays are hopefully minimal on modern systems

The delays are almost always self inflicted by people who've blindly put 36400 in the TTL field like some sort of magic charm rather than considering how long they want the cache expiry to be. Long ago I was one of them and then I had the company greybeard point out that DNS record updates are a thing we had control over - just drop the TTL to 30 seconds or whatever a day before a planned change of servers and (barring the odd stubborn resolver which thinks it knows better than you do) the time it takes for those caches to refresh goes from 24 hours to 30 seconds.

[bux93]

djbdns/tinydns can schedule a change and give out a lower and lower TTL the nearer the changeover time gets - a quick search doesn't show any newer implementations but this is surely a good way to do it.