Maybe-useful shell oneliners #n:

(date +%s; read foo; date +%s; echo r - p) | dc

Press return to start the timer, press return again to stop it and get a rough time in seconds between the two presses. May require GNU date, as I do not know how widely spread "%s" is as time-in-seconds-since-epoch time format control.

Sadly, the first version did the subtraction and then multiplied by -1, but I think properly swapping the two top elements of the stack is a slight win for elegance (if piping things into dc can ever be called "elegance").