Automatic shutdown triggered by inactivity

I am running ReadyNAS Ultra 2 mainly as a file server and sometimes as a media server for private use. I do not need it awake around the clock nor power on/off as scheduled. I just simply want it boot up by WOL and shut down silently after, lets say, 15 min of inactivity.

I fully agree with ehgeahrev (Automatic shutdown of readynas pioneer pro?). He solved his problem by using Curl and I myself tried the same method successfully. But, still, I think his idea of shutdown by inactivity will be nicer for people who are keen to power saving.

In that thread, chirpa referred to the comlexity of checking before shutdown. But, spin down by inactivity is already implemented. So, I wonder if it might be possible that ReadyNAS automatically shuts down when, lets say, 10 min has passed after it goes into spin down mode.

Why not just satisfied by spin down? It is because I found spin down does not dramatically cut power consumption. My Ultra 2 (with two 2.5-inch hard drives) consumes around 22W when actively working and 18W in spin down mode. It is far from what I had expected.