Which sequence best supports a DNS address migration with a previous TTL of one hour?

Which sequence best supports a DNS address migration with a previous TTL of one hour?

1. Change the address and immediately shut down the old endpoint.
2. Lower the TTL in advance, wait out the previous TTL, overlap healthy endpoints, then observe traffic before retirement.
3. Set TTL to zero after the change and assume existing connections move.
4. Keep the one-hour TTL but ask clients to flush every cache simultaneously.