> I'm actually surprised that there's so little visual consistency there...

The Stopwatch and Timer start buttons behave differently.

The timer provides some visual feedback because it starts the timer when you take your finger off the screen, you can touch and hold the button all you want but nothing happens until you release it.

The stopwatch on the other hand starts as soon as you touch the screen. I can see how that would be useful if you're timing a race or something that takes less than a second.

Incidentally, my double click/touch interval seems to be averaging around 0.12 seconds :)