The rules write the timing when the game starts,but i saw level 1 no1 the timing starts after a short black screen after clicking the first level of the game.Didn’t it start timing when you clicked the first level?

You are correct, for the levels you should start the timer after the black screen fades into the level not upon clicking it. A timer is not necessary to do a speedrun as I will always retime it to get an accurate time.