If you only want to trigger the notification once, easiest way would be a sequence expression.
Like FrontDoorOpened and (FrontDoorOpened;!FrontDoorOpenCloseTimer)
In this case I only want a notification if the door has been left opened for 10 minutes. When the Front Door is opened I start a 10 minute timer. I only allow the condition triggering a notification (above) to fire after that 10 minute timer has expired. (In this case it will only notify once, even if the door is left open for hours. There is another more complicated way if I want periodic reminders it is still open.)
In your case, take the existing condition, and add an action to start a self-re-triggering timer. Manually start and end that timer (toggle). Then modify the existing condition to only fire if the timer has stopped before the current senor trip timestamp.
(@kigmatzomat 's Now example above is a LOT easier to implement, but timers AKA schedules take less overhead and give you more control.)