There will be many factors at play here. Cloud based providers may use their own protocol to sync between primary ns and ns1, ns2. Default TTLs might be shorter

There will be many factors at play here. Cloud based providers may use their own protocol to sync between primary ns and ns1, ns2. Default TTLs might be shorter and caches may well cache for less time; also cache invalidation. If you provide more information about the type of DNS server, who controls it, how it is managed and any default TTLs, perhaps people can help explain the shorter propagation period.