Work out dns ttl propagation time instantly with clear inputs, formula shown and shareable results.
DNS changes propagate at the speed of the cached TTL, so lowering the TTL must itself happen one full old-TTL period in advance. Compliant resolvers then update within the lowered TTL, but a small share ignore TTLs and cache for hours, which is why the old endpoint must keep serving until the worst-case window has passed.
Propagation timing
lead time before change = old TTL; propagation = lowered TTL; worst case = over-caching resolver hold time
Because resolvers that already cached the record hold it for the old TTL. Lowering it takes effect only after that period expires.
No. Keep it serving or redirecting for at least 24 to 48 hours, because some resolvers and hard-coded clients will keep using the old address.