"The idea of starting the shot time from when flow begins is useless to ludicrous."
It is neither, on the contrary, it is extremely useful to keep tract of the time between pump activation and the visibility of the first drop. The length of this time, however, will be in relation to the style of shot you pull, the flavor you are looking for, the type of machine you use.
You can certainly make the point that one shot may be drinkable with a 4 second "pre-visible" time, and another can be drinkable with a 12 second "pre-visable" time. But a skilled Barista who exhibits great consistency will always have near identical "pre-visable" intervals. I am not saying that this interval needs to be same for everyone, but it should be the same for everyone in one shop.
I strongly believe that there is an advantage to knowing this piece of information. All by itself, it is not a complete picture, and in relation to other styles of shots, or with other espresso blends or SOs it will change. Everyone is free to start counting whenever they feel like, but you will be missing out on something if you wait till you see coffee.
Chris, your first post read like you stopped timing when it blonded, regardless of when you stopped your extraction. This isn't a discussion about when to stop your extraction, it is about when to start timing.