The honest answer: it depends on the TTL of the old record. If the record had a TTL of 3600 (1 hour), resolvers cache it for up to 1 hour after you make a change. After that, they fetch the new value. Most of the world sees changes within 1-4 hours for typical TTLs. ‘Up to 48 hours’ is often cited but is rarely relevant today — it applied to old root zone update schedules, not typical record changes.
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