TTL (DNS)
A DNS record TTL sets how long resolvers cache it. Short TTLs allow fast cutover; long TTLs save queries and smooth over name server outages.
In practice
The classic migration move: lower the TTL the evening before, cut over, raise it once stable. Forgetting the first step means waiting for the global cache to expire — sometimes twenty-four hours with the site half-migrated. Standard values: 300 seconds during change, an hour or more in steady operation.