I think most people who choose to commit suicide have given it a good few months or more of thinking. How long do people have to suffer in order for you to say "this person's done enough thinking about it, he can go"?
Speaking from experience, I disagree. I'm in favor of a generalized right to commit suicide as a fundamental ground of self-determination, but it can often be a compulsive rather a considered action; furthermore it can be based on a fundamentally irrational discounting of the future ('I'll never be happy again, my life can only get worse') which may be merely temporary or the result of developmental delays/deficits in handling emotional swings.