There's no rule on this--use some long-lost common sense. Your looking down the runway, it's clear, checklist is complete and PM is ready to go, you get the clearance, push up the throttles and go. I'd wait until ATC has the learance out, so as not to jump the gun.
Has aviation training now reached the point we need a rule for English fluency? How did you depart without ATC giving you a clearance?