nope, it would stay on all night and still be doing it in the morning.
however, i fixed it...in a way that makes no sense. i first reset the monitor to default settings, then manually set a sleep timer. any timer at all works. i set mine to go to sleep at 3am, for example.
now, the monitor functions like it used to: if the computer turns off, the monitor displays "no signal" for 30 seconds, and goes to sleep.
no clue how that solved anything, but there you go.