Adjust timeout for "Delivery delayed" notification to less than 24 hours?

Recently a hosting customer has mentioned an issue with outgoing EMails that can't be delivered, but don't hard-fail - and are instead held in the queue to attempt re-delivery. The issue is that this customer is using a system to send out appointment reminders & has had a few problems where there was a typo in the address the reminder was sent to (specifically in the mail domain, so the server was trying to deliver the message to a host that didn't exist) - but because the server doesn't send a notification until 24 hours had passed, our customer didn't get notification that the message couldn't be sent until AFTER the appointment had passed. Is there any option in WHM to send an immediate notification when delivery is delayed (ideally configurable per-sender, or at least per-CPanel account) - or at least decrease the amount of time before the first "delivery delayed" notice is sent to something more reasonable like 1 hour? I can't find anything in the Exim config in WHM or in Tweak Settings. I have found some documentation for doing that directly via Exim's config - but I usually try to avoid going "under the hood" with anything managed by CPanel, given that it seems to be a coin-toss as to whether the next CPanel update will destroy/overwrite that. Any suggestions?