Migration downtime is a scheduling failure dressed up as a technical one. The file copy takes an hour. The database export takes ten minutes. What takes the site offline for a day is a name server record that was changed at 4 pm on a Friday with a 24 hour cache lifetime attached to it, by someone who had not been told that the marketing team was publishing a campaign that evening. The project manager owns that sequence, and the sequence is where the outage lives.