Request for Enhancement - Notifications - Hub Variables

Use case:
I am trying to use a Hub Variable in Notifications, as the limit for the amount of time that a contact sensor can be open, in order to trigger the Notification.
Sample Screenshot:


Instead of a fixed number of minutes ("for how long"), I'd like to use a Hub Variable which I created.
Summary:
Make the built in function"Notification" Hub Variable aware.

Note:
Even with Rule Machine I can't use a Hub Variable for the length of time a contact sensor is open:

Does anyone have any suggestions on how to do this particular situation in RM?

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