Propagation of amazon.com.

A DNS change takes effect at your DNS host at once. What takes time is every resolver around the world that already asked: each keeps its copy for the record's TTL, then asks again and gets the new answer. "Propagation" is those copies expiring one by one. This page asks 13 public resolvers, run by different companies, and shows what each holds now and how long until it asks again. The first row is the zone itself: one of its own name servers, asked directly with no cache in between, so it shows the answer every resolver will hold once its copy expires.

• A day before a planned change, lower the record's TTL to five minutes. Old copies then expire within five minutes of the switch.
• After the change works everywhere, raise the TTL again (an hour or a day) so resolvers ask less often.
• A record that did not exist before can still be cached as "does not exist" for the zone's negative TTL: the last number of its SOA record.

New name servers are set at the registrar and cached by resolvers from the registry, often for a day or two. Pick NS in the type menu to see which name servers each resolver still uses, and keep the old DNS host serving the same records until they all agree.

Large sites answer with different addresses in different places (geo DNS) or rotate them (load balancing). Several different answers with very short TTLs, with no change of yours behind them, are that, not a problem.