Timing seems to be one of those big things that distinguishes the rookies from the vets. Wait too long and people think you are not sure, bang it too quick and you miss things like in the above. I've been told to take a breath. Any other suggestions?
I tap the outside of my left thigh with a closed left hand - it's almost like a timer, I guess.
If I am to quick I will silently clap my hands once or twice to remind myself to slow down.
I know I'm coming into this a bit late . . . sorry.
I would respectfully suggest you discontinue the use of all of these timing mechanisms and go with what mstaylor advised, or something very similar.
Artificial timing mechanisms are just that - artificial. They don't help you make decisions, they just slow you down a little bit which seems good, but really has no positive affect on your game.
As has been said here, and on other boards, many, many times: Timing is the correct use of your eyes
There are different ways to describe this, and none of them are perfect but I would recommend watching the play, briefly reviewing the play in your head to ensure a correct decision, and then make the call. Don't let the delay between the play and your call become a vacuum - use that time.