Nothing switches over until the checks pass
Your site is copied and tested on a temporary address first. The switch-over is offered only when the preview check (your copy compared with the old site) and the app check (everything arrived and the site answers) have passed. Click through the preview yourself too — pages, forms, checkout, the admin area.
Your GO
Reply GO on the ticket, or press Switch over now (GO) on the move's page in Migrations. A reply that only mentions "go" inside a sentence is not taken as your go-ahead. You can also say when suits you best in the form; the switch-over still waits for your GO.
The DNS change
⭐ Lower your domain's TTL to five minutes a day before, so the change takes minutes and is just as quick to undo.
Email
If you moved email, the last messages that arrived at the old host are copied across at the switch-over.
The live check, then DONE
After the switch we check your own domain really serves the new site — DNS, any CDN and our servers. Only then is the move marked done on the ticket, with what was moved. Keep the old hosting for a couple of weeks: it is what lets you point back if you ever need to.