What is DNS TTL and what should mine be?

TTL is how long resolvers may cache a DNS answer before asking again. It sets how quickly a change takes effect:

• Long TTLs are efficient - fewer lookups, and resilience if your DNS provider has a wobble.
• Short TTLs are agile - changes propagate in minutes, which matters during a migration or a failover.
• An hour is a sensible default for records that rarely change.

Drop the TTL a day before a planned migration, then raise it again once the change has settled.