TTL

TTL stands for time to live, and in DNS it is a number of seconds attached to every record. It tells any resolver that receives the answer how long it may keep serving that answer from memory before checking again. It is set per record, so a hostname can be nimble while the rest of the zone stays slow.

The trade is direct. A low value such as 300 means a change reaches everyone within five minutes, at the cost of more lookups. A high value such as 86400 means a day of stale answers after an edit, in exchange for fewer queries and a slightly faster first connection for repeat visitors. For a short-link hostname a moderate value is fine: the lookup happens once per visitor per interval, and the redirect itself is unaffected.

The rule that saves time is to lower the TTL before you need it, not while you need it. A reduction only takes effect once the caches holding the old answer expire under the old value — which is the whole of what people call DNS propagation, and why the domain connection guides suggest doing it a day ahead.