I have heard that Tylenol could actually take about 2-5 days to effectively cause liver damage. There have been cases where people have overdosed, gotten their stomachs pumped, and died a few days after medical treatment. I would seriously hope that treatment methods have been improved since those cases.
http://en.wikipedia.org/wiki/Paracetamol_toxicity
I would pay close attention to the "signs and symptoms" section. This doesn't sound like the most pleasant way to off yourself.