Thanks for the assistance and trying to validate my findings. I did some more testing and these are my findings with my C-5 on Platform Version 2.4.3.176
NOTE: I noticed a few changes to Hubitat since my posting a year ago......there is now an Update HSM button and also you canNOT Cancel a Pending alert manually from HSM, the Cancel Alerts button doesn't show up in HSM until after the intrusion delay is over.
1-DELAY INTRUSION alerts only for selected doors
It appears that if you toggle the "Delay intrusion alerts only for selected doors" or you make any changes to which doors you have selected or the timeframe and fail to click the Update HSM or Done with HSM buttons on the subsequent page it will disable the intrusion delay entirely even though it will still show all the changes you made in the "Configure Arming/Disarming/Cancel Options" section of HSM.
Also if you were to open the "Configure Arming/Disarming/Cancel Options" section of HSM without making any changes, and then you close out the browser tab, the intrusion delay will no longer work.
If you de-select the "Delay intrusion alerts only for selected doors" and make changes to the time without clicking on any other buttons and even if you close the browser tab, the intrusion delay will work.
2-Auto Alert Cancel with PENDING Alert disables Future Alerts
Canceling an alert via HSM manually or via a rule after the alert has been issued both allow subsequent alerts.
Canceling a "pending" alert via a rule will prevent you from receiving that alert and all future alerts without manual intervention.....HSM will just be stuck with a "Delayed intrusion alert pending".