Flip the switch
Going live usually means updating a DNS record to point at the new site. The moment you save it, the internet slowly starts using the new address.
Propagation takes time
Changes don't apply everywhere instantly — networks cache the old answer for a while. This spread-out update is called propagation, and it can take minutes to a day.
Don't panic if the new site shows for you but not a friend — that's propagation catching up, not a broken site.
TTL controls the wait
TTL (time to live) is how long networks are told to remember a record. Lowering TTL a day before a big change means the switch happens faster.
Key takeaway
Lower the TTL a day before a big change so the switch-over happens quickly.