Realistic timings.
A RECORD CHANGE
Up to the previous TTL. If that was four hours, allow four hours.
With a TTL of five minutes, usually minutes.
A NAMESERVER CHANGE
Usually within an hour. Occasionally up to forty-eight.
The registry updates quickly; resolvers holding the old nameservers take longer.
A NEW DOMAIN
Usually under an hour once nameservers are set.
A ZONE ADDED AT A NEW PROVIDER
Immediate on that provider. Visible to the world once nameservers point there.
WHAT MAKES IT FASTER
Lowering the TTL in advance. That is the only thing you control.
WHAT MAKES IT SLOWER
A long TTL on the old record Resolvers that cache longer than instructed Your own device's cache
HOW TO TELL WHETHER YOU ARE WAITING OR BROKEN
Query your authoritative nameservers directly.
If they return the correct answer, the change is made and you are waiting.
If they do not, something is wrong and waiting will not help.
THAT SINGLE CHECK
Answers the question definitively, in thirty seconds.