Supposedly three days.
About three days. Supposedly painful.
Other ways likely more painful. Plus it's free, gives you a little time to change your mind, make plans, if you screw up it doesn't take your face off while still living (guns), not messy... think it over.
About 19 days I think.
If you don't consume any fluids at all and you're in a very arid, dry environment and intense sunlight -like in a desert- it can happen in less than 24 hours.