What is TTL in DNS?

What it is

Every DNS record has a TTL, measured in seconds. A TTL of 3600 means that other servers can reuse their saved answer for one hour before asking again.

Why it matters

TTL is one reason DNS changes don't appear everywhere at once. A server that saved your old record may keep using it until its TTL runs out.

When to lower it

If you are planning a move, lower the TTL a day or so beforehand. For example, setting it to 300 means a saved answer lasts five minutes. The change then spreads more quickly on the day, and you can raise it again afterwards.

Lowering it only helps once the old, longer TTL has run out, which is why it needs doing in advance.