A DNS record change isn't instant everywhere, because of how caching works across the recursive resolvers described in Public DNS vs. Authoritative DNS. Each DNS record carries a TTL (Time to Live) value: a number of seconds that tells any resolver caching that record how long to keep serving the old answer before checking again.

In practice, that means:

• A resolver that already cached your old record won't see the change until its cached copy's TTL expires.

• Lowering a record's TTL well before you actually make a planned change is a common way to shorten this wait, since it gives caches less time to hold onto the outdated answer.

• Changes to major gTLDs like .com , .net , and .org are commonly visible within minutes to a few hours in practice, while some other TLDs can take longer, up to 24–48 hours in less common cases.

This is also why a DNS change can appear to work for some people and not others at the same time; they're hitting different recursive resolvers with different cache states, not seeing different actual records.