End of game

[som44]

Situation. Team A down by one--8 Seconds to go in game-Team A inbounding ball after a basket by team B--Team A Inbounds and team A player quickly gets around his defensive player-dribbling to mid court with an advantage ie 5 on 4--you notice the clock has not started--since you are counting down for a ten second violation you have definite knowledge of time elasped--do you blow whistle as soon as you notice clock and stop Team A's advantage?
It seems the only right option to me--what else can you possibly do? or what should you do?

thanks