Taken from this (https://msdn.microsoft.com/en-us/library/windows/desktop/aa383561(v=vs.85).aspx) article:
"By default, the user is considered absent after four minutes of no keyboard or mouse input."
I find it interesting that it mentions this setting is "by default". Is it possible to change that value? Since the "Start the task only if the computer is idle for:" condition is apparently broken in 8.1, I would find this setting to be a nice alternative to being able to customize the amount of time to wait before executing a task.