Not Medical Advice: A study of suicide attempts in adults has shown that the amount of sodium hypochlorite (bleach) and time it takes for a dose to be lethal can vary widely. It could take anywhere from a few hours to many days and would be extremely painful.
Bleach will corrode your mouth, esophagus, and stomach, eventually dissolving all of your internal organs. It can also cause nausea, vomiting, diarrhea, excess mucous production in the eyes and long term damage to the central nervous system.
Of interest: A recent trend is to try to beat a drug test by ingesting bleach - which does not work and is dangerous.