It depends!
The length of time it takes to move a website and its associated mailboxes depends on the amount of data being transferred and the complexity of the website. Some migrations can take up to six hours, although the average time to migrate is 60 minutes.
While a migration is in progress, you’re free to close the tab and carry on with whatever you need to do; the migration will complete independently.
You’ll receive an email informing you when the migration is complete.