When you change a DNS record — pointing a domain to a new server, for example — that change doesn't appear everywhere instantly. Here's why, and what you can do to make it faster next time.
It comes down to caching
Every DNS record has a TTL (time to live), measured in seconds. Resolvers across the internet cache your record for that long before checking again. If your A record has a TTL of 86400 (24 hours), some resolvers may keep serving the old value for up to a day after you make the change.
What you can do
Lower the TTL on a record a day or two before you plan to change it. Once the low TTL has had time to propagate, make your change — it will now spread much faster, since resolvers won't cache the old value as long.