DNS TTL & Cutover Planner

Lower the TTL to 60s at least 1 hour before the change, make the change at Wed, Jul 8, 08:53 AM, then expect full propagation within 2 minutes.

1. Wed, Jul 8, 07:53 AM
   Lower the record's TTL to 60s
   Do this at least 1 hour before the change so the old 1 hour TTL has time to expire in every resolver cache.
2. +1 hour later
   Old TTL has fully aged out
   By now every cached copy uses the new 60s TTL. Resolvers will re-query at most every 1 minute.
3. Wed, Jul 8, 08:53 AM
   Make the DNS change
   Update the record value (IP, CNAME, etc.). Caches now refresh quickly thanks to the low TTL.
4. Wed, Jul 8, 08:55 AM
   Change fully propagated
   Worst case is 2 minutes after the change (new 1 minute TTL plus resolver slack). Once verified, raise the TTL back to 1 hour to cut query load.