I think it depends on how severe your stutter is. If u cant get out 2 words without stuttering, you should tell him earlier. If most people dont know them just keep it to yourself. Ive been with my girlfriend for 5 years and i didnt tell her I stuttered and the first time i stuttered I was trying to spell my name at a car shop and laughed and made fun of me. Then I told her and she felt really bad. So it depends on how severe your stutter is (mine is mild) and it might also help them be more empathetic/not think its something to laugh about down the line