I believe the correct answer is "whenever it is least convenient for you or most disruptive".
Seriously, though, it totally depends on the individual roo. Perhaps you will get lucky and he will be a quiet one when he does start. Me, not so much. Never knew so much noise could come from a little Silkie!
Mine just started to crow at 23 wks. I was hoping he didnt have a voice lol Nope. He now crows but luckily not to much so I put him in the garage in the early morning, turn on the light, then he stops and goes outside by 9am