Well, it's a good point. Most of the time, my notes are taken at tastings, not actually sitting down at the table with a bottle, and while I may note that a wine probably needs decanting, I'm just guessing as to how long.
There are exceptions: I remember the '02 LeFlaive "Cuvee Margot," back when you could still get a decent Bourgogne for fifteen bucks. I tried it with one hour, two hours, three hours, and four hours time in the decanter, and decided that 3 hours was about right.
Another was a Grumello, can't remember whose at the moment, but it was an '01 and tight as a tick. Two hours was the minimum, and frankly, it didn't really get its legs under it until the next day!
One last, and I'll never forget it, because it was a white: Nigl Gruner Veltliner '99. The way to go was to open it on the morning of the evening you wanted to drink it, pour it into a decanter, pour it back into the bottle, put the cork back in, and leave it in the fridge for at least eight hours.
Now that I think about it, maybe this is why I don't mention decanting in my notes. People will think I'm nuts.