Hi @Chris M,
Based on your description, I understand you had a concern about if enable SSL offload load balancer and domain secure connector meantime make a difference to the delay of email.
Offloading should only be enabled when you're running a hardware load balancer, and you're happy with how you've got your network secured, and your Exchange Servers would benefit from the reduced overhead of not having to perform SSL decryption.
However, the Offloading should be disabled when you need connect directly to an Exchange Server over HTTPS and it is not supported with a TLS protected connection.
You could kindly disable the SSL offload and then enable the domain secure connector to see if it works.
Hope the information helps and if you have any questions, please feel free to contact me.