When changing a record, it will take the length of the TTL (time to live) in seconds to expire before your new changes go into effect. You can set the TTL to any value before or after making changes to your records. Reasonable values for a static IP are anywhere from 12 hours (43200 seconds) to 24 hours (86400 seconds). Reasonable values for a Dynamic IP are between 5 and 120 seconds.
Domains that use Secondary DNS are scheduled to be added to the secondary DNS services no earlier than 2 hours after you enter the data into the system. This provides enough time to configure your primary DNS servers to allow AXFR/IXFR transfers to our secondary name servers. You should allow at least 48 hours for configuration changes to propagate before removing any previous name servers.
To confirm the changes,
Go to http://mxtoolbox.com
Specify the domain name
Verify the MX and TXT records.