Kneeling Cornertime Stress Position With No Clock

Fully nude kneeling corner-time is already humiliating, but with my hands behind my head like this, the position gets difficult really, really fast. It's all made so much worse by knowing I've got to do a full half hour, but that because I can't see the clock, I've got absolutely no idea how much longer I'll have to endure this difficult position. I'm trying to keep count of the minutes in my head, but it's really, really difficult!