Countdown or start button before a fast interaction
I'm currently designing a small mobile application which requires fast clicking. Among other things, it measures how many times you can click in 30 seconds. I am not sure what put between a preparations screen and an interaction screen. I thinking about 2 approaches.
Countdown. On the down part of the preparation screen there is an instruction for interaction screen and the Start button. When User click Start it shows the interaction screen with the countdown in the middle. 3, 2, 1, 0 and the fast interactions start.
Start button. On the down part of the preparation screen there is an instruction for interaction screen and the interaction screen button. When you click the button you jump to the interaction screen with the Start button in the middle. Once you click it you start the interaction. The clicking starts in the middle on the screen, so your finger is already at place. Also it will be counted as the first click.
I should also add that interaction will always start from the first click on the interaction screen. So the countdown is there only to calm down the user. (There is countdown and after it ends system stil wait for a user response.) It can be kept in the mental model by not informing user that system is waiting for him/her to start. After all most people will start the clicking immediately after the countdown... Does this make seanse?
Also most users won't use this function more than once or twice.
I see pros and cons of both solution and it is hard for me to chose one just using logic. Thanks in advance.
*I can't tell you exact name of the button because my client asked me to keep the project a secret. Also I don't think the name is relevant. However the name isn't vague and it is shorter.