DNS propagation

DNS servers around the world cache records for the length of their TTL. Until those copies expire, some visitors still reach the old server while others see the new one. It can take from minutes to a day or two.

A nameserver change often takes longer than changing a single record, because the details of which nameservers a domain uses are often cached for longer.

Example: you change the A record for yourbusiness.com on a Monday morning. Visitors whose internet provider cached the old record an hour earlier keep seeing the old site until that copy expires. By the next day almost everyone reaches the new host.

That's why your old site should stay live until the move is complete, and why you shouldn't cancel your old hosting the moment you change DNS. Lowering the TTL a day before the move shortens the wait.

What it means for your price: keep your old plan running for a few days after the switch. It's a small overlap that protects your orders and email. Time the move for shortly before your renewal date, so the overlap doesn't turn into a whole extra term.