Sorry I must have misinterpreted what you needed.
Still, if you really need it to shut off quicker, and I know I'm going on a limb here, but why not just hit the power button?

Incidentally, that 40 seconds, I'm pretty sure includes the 10 seconds already spent on dimming the display. I say that because I know I don't wait 5 minutes for mine to power off (2 min standby and 3 min power off).