Minutes. Fleeting thoughts of hearing one's name called or isolated episodes of thinking you hear or see something may be normal. Anything else is a symptom of abnormal brain activity. Psychosis is a formal thought disorder which includes hallucinations, delusions, and disorganized thought patterns. Hallucinations can be caused by many things. Talk to your doctor.
Not long! But psychosis is only a symptom that can be caused by a number of things including drugs, medical issues and psychiatric issues. See you doctor now.
Depends. There is no specific timeline in which a psychosis is determined. It really depends on how the symptoms are affecting you. If you are seriously troubled by the voices or things you see or believe, seek help immediately. If it has led to drop in function (like not going to work or isolating from friends and family or leading to urges to follow through with the hallucinations) then seek help.