How quickly changes take effect.
WHAT TTL IS
How long a resolver may keep a record before asking again.
A TTL of one hour means changes may take up to an hour to be seen everywhere.
AT CLOUDFLARE
For proxied records, TTL is managed automatically and the setting is unavailable. Changes take effect almost immediately, because the address does not change; Cloudflare simply routes differently.
For DNS-only records, you set it.
BEFORE A PLANNED CHANGE
Lower the TTL a day or two in advance, to five minutes. Then the change propagates quickly when you make it.
Raise it again afterwards.
This is the standard practice before a migration and it is worth the small effort.
WHAT PROPAGATION ACTUALLY MEANS
Resolvers around the world holding cached copies until their TTL expires.
Nothing is being pushed anywhere; old copies are simply expiring at different times.
WHY SOME PEOPLE SEE THE CHANGE AND OTHERS DO NOT
Different resolvers, different cache states. This is normal and resolves itself.
CHECKING
A DNS lookup tool showing results from several locations tells you how far the change has spread.
