Would it be possible to add a checkbox beside the "start/stop" hotkey setup that, when checked, changes it to a "start" key only? This would minimize the possibility of the clock being stopped accidentally during an event because it would require the use of the mouse to stop it.
In case you're wondering why I'm making this suggestion - instead of just using the mouse to start the clock and avoid using a hotkey at all - it's because at a race I often have to keep an eye on several things at the same time and it's easier to just tap a key than look down to make sure the mouse cursor is on the "Start" button. I'm often standing a few feet away from the computer with a wireless keyboard or keypad in my hands.