As I mentioned before, the wake timer you saw with powercfg /waketimers is for the next TV recording, and had no bearing on why you could not put the system back to sleep. The wake timer we use for TV recording is non-repeating, and remains signaled once it has been signaled. So the old timer should not prevent the system from going to sleep, even if the older timer was not cleaned up. In addition, we do clean up the old timer at the time when the system tries to go to sleep again, in order to setup new recordings.
In one of my replies above, I mentioned that my system kept waking up last night, a few minutes after it was put to sleep. What I discovered today was that it was caused by a mulfunctioning TV hardware (Hauppauge HD PVR2). After it has been running for a few days, it would go into a non-responsive state, with Windows not recognizing the USB device. That was what kept waking up the system. Maybe you have a similar situation?