DNS, firewall and Exchange inbound email

I recently obtain new IP block for replacement the old IP block is still active and I was trying to start making change from Exchange before I change SQL.
The external interface and VPN on firewall has different range therefore it does fall under the range I am changing.

For exchange I have changed the A record for mail server and auto discovery with new address. Reduced TTL to 10 mins and saved as 30 mins I though was long, therefore, I reduced TTL for A record of mail and autodiscovery and saved the changes again
In securence I replaced the delivery address with new IP
I changed the 1 to 1 NAT on watchguard firewall with new public for mail server

It has been half and inbound mail is not working, When I run test connection on securence it shows "could not connect on new ip to port 25" and it has not gone to maintenance and still shows delivery status.

When I ping old IP is still get reply though it does resolve to mail server name when I query from mxtoolbox, which means changes are applied but when ping new ip address it requests timed out. It has been almost 5 hrs after the changes