I'm now on my second Mac with the same problem. I want to schedule it to switch itself on at 6am and turn itself off at 11pm every day. Switching on works fine but turning off doesn't. It will always turn off an hour early unless I interrupt it. If I do interrupt it there is a 50/50 chance whether it will turn off at 11pm or stay on all night. My original machine was a 27" iMac with Snow Leopard which I subsequently upgraded to Lion. This was recently replaced with a 2011 Mac Mini which came with Lion but still has exactly the same problem. Does anyone know of a solution to this problem please?