How long does a DNS change take? Understanding TTL and planning properly

Anyone changing a DNS record for the first time is often surprised: on their own phone the change already works, on the laptop next to it not yet. That is not a bug but intentional. DNS answers are cached.

What TTL is

Every DNS record has a TTL, a lifetime in seconds. It tells caches how long they may keep the answer before asking again. With a TTL of 3,600 seconds, a device may keep using the old answer for up to an hour.

New records versus changed records

• A brand-new record, such as a TXT verification, is usually visible within minutes because nobody has cached an old answer yet.
• A changed record, such as a CNAME that previously pointed elsewhere, only takes effect everywhere once the old TTL has expired.
• Some providers themselves need a few minutes before a change made in their interface appears in DNS.

How to plan a switch without downtime

• A day before, set the record’s TTL to a small value, such as 300 seconds, if your provider allows it.
• Switch when few people are scanning; in hospitality, not in the middle of lunch service.
• Test straight afterwards with a phone on mobile data, not only on your own Wi-Fi.
• Once everything works, set the TTL back to the usual value.

Why domain moves hardly cause gaps

When a subdomain with QR codes moves from one service to another, both answer scans during the transition: devices with the old answer still reach the old service, the others already reach the new one. The only important thing is not to cancel the old subscription on the same day.

How to check the status

Public DNS check sites query from different places around the world and show who already gets the new answer. In the Same-QR dashboard, “Check status” shows whether the connection is in place.

Frequently asked questions