Will my sites go down while they are being moved

They should not, and zero downtime is the expected result rather than a lucky one. The reason is the order of operations: everything is copied while the old site is still serving, the copy is verified on the new account, and delegation is only changed once the new copy answers correctly. At no point does the content exist in only one place.

Why the sequence matters more than the speed

Most migration horror stories come from doing it backwards. Change the delegation first, then copy, and there is a window where real visitors reach an empty or half-populated account. That window is entirely self-inflicted and it is the one thing a careful sequence removes.

Copying first also means the fallback is free. If the verified copy has a problem, nothing has been switched yet and the old site is still serving as it was. You are never in a position where rolling back is itself an outage.

What can still cause a visible gap

Being honest about the edges is more useful than promising perfection:

• Long record cache lifetimes. If your DNS records tell the world to remember them for a day, some resolvers will keep sending visitors to the old address for up to a day after the change. Lowering that value before the move, not after, is the fix.
• Hardcoded addresses. Anything in your application, a firewall rule or a third-party integration that names the old address explicitly will keep pointing there.
• Mail in flight. Messages delivered to the old host between the copy and the cutover need collecting.

None of these are surprises if they are checked beforehand, which is why the pre-move questions are worth answering properly.

How to verify rather than hope

1. Load the copied site on the new account before any delegation change, using a hosts-file override so you see the new server without the world seeing it.
2. Exercise the parts that break quietly: forms, logins, anything talking to a database.
3. Lower the record cache lifetime at least a day ahead of the switch.
4. After the switch, confirm from more than one network that the domain resolves to the new address.

The hosts-file step is the one people skip and the one that catches the most problems, because it separates "the files copied" from "the site works".

If it does go wrong

The old copy is still there until you remove it, so reverting the delegation is a genuine option rather than a theoretical one. Keep the old account until you are satisfied, and do not cancel it the same afternoon. The platform availability commitment and the money-back window are described on why choose us. Sequencing for a whole estate is in Migration Basics.