Mxroute is probably dealing with that due to large queue volumes and insufficient resources. We are focused on providing fast delivery, however any real mail admin would know that a guarantee is not possible with the way SMTP is right now.
We have excessive resources as well as our own IP ranges. Any delays are most likely related to someone else. Can’t send someone email faster than their mail server accepts it. Happy to answer a support ticket about it but all of our mail queues are human audited every few hours.
Best wishes for you and your startup, we need more good people out here.
Edit: There is one exception being one older server that is experiencing a bug specific to cPanel, which is mitigated presently with a final resolution in progress. That’s just sysadmin stuff.