Help making a timed pressure release that can have time accuracy of tenth/second

[razvan]

This is for a game where you press a button release it when you think is right to hit a very small target. The gadget would go between my hand and the button and once pressed against it activates the timer and releases at a preset time such as 2.4 seconds. I also need to be able to adjust this easily because it would take a couple tries to figure out the perfect time for each target hole. In my opinion the best way to do this is to have a iphone app that you can type in the release time and its connected to a pneumatic release or something similar which then starts the countdown once I press it down with my hand. The longest time it would be set to is probably 8 seconds so if you think it can be all mechanical without the software, than great. Also any other ideas are appreciated. Any help is greatly appreciated and If I can sort this out I will post a video of the result.