Trigger duration when wattage is below threshold for a period of time

I’m trying to configure an automation to turn off my 3D Printer when idle for 15minutes. During operation my Sonoff says the wattage jumps between 40-200watts when printing so I figured I set a trigger for when Power is below 10 Watts for a duration of 15minutes. Once it was all done I watched the printer work for 15minutes and then shut down even though it was printing and the wattage was a lot higher than 10 Watts. Am I not understanding the duration piece of automation or is this not possible?

It probably is possible but without the automation we can only guess