I’m going to take a stab at this.
I’m going to create a virtual switch named ‘Things Quiet Down’. Then I’m going to create a Smart Lighting Automation that turns On the Things Quiet Down virtual switch triggered from any or all of my motion sensors and then set it to turn Off the virtual switch after 15 minutes. I’m then going to create an Automation that if during the time window set, and the Things Quiet Down virtual switch is off, then enable the STHM.
I just tested it, and it seems that Smart Lighting will continue to reset the 15 minute countdown if the virtual switch is already on whenever motion is triggered from any of the motion sensors selected. Cool!
And, the Things Quiet Down virtual switch should also work for when Things Start Happening too. So, I changed the name for my virtual switch to ‘Things are Quiet’.