Around 11:20, O Sensei and his son are practicing a kata. It isn't something I was taught as an Aikido kata, but it has some interesting timing lessons. Kisshomaru Ueshiba doesn't even get his sword clear of the scabbard before the kata concludes. He moves, and O Sensei is already closing the gap and striking.
Of course, the whole documentary is worth watching so don't just jump to the end.
Some of our own Tachidori is influenced by Hollywood gun fighters I think. The idea that until the first guy draws his weapon, we don't have the right to respond. Sort of a "Who Threw The First Punch" mentality. The first punch is from the villan/guilty party, and the responder is the hero. The threats, the resorting to weapons,the escalating danger is clearly on the person with the sword against the unarmed man. Some of our self defense laws in the USA are interpreted by this Hollywood standard, at least by the general public.
Kawahara Sensei would sometimes say, "Don't move until the sword is descending and committed." Sometimes we were to move the second the sword started to raise.
Once, a sempai of mine who was training in Filipino knife fighting asked Sensei what he would do against an attack he'd been shown. His hand quickly went to his belt to pull his imaginary knife, and before he managed to make his pulling motion, Kawahara Sensei made an amazing fast Shomen Ate type entry, grabbed the "knife hand" and punched his student's solar plexus lightly. No waiting for the slashing movement, no waiting until the "weapon" was pulled; Sensei started his defense/counterattack instantly. The same timing that O Sensei and his son are demonstrating above.
I referenced this clip in the last Tachidori class as an extreme example of moving early. Not all of my Sensei's tachidori (nor O Sensei's or anyone else's) only happened in response to a fully drawn sword descending on Nage's head. This is necessary timing to practice, but it isn't the only timing. This has implications for empty hand practice too - as a beginner, we only have you respond to the attack but as time goes on you are expected to be more comfortable with "Ki Flow (Ki no Nagare)" and even initiating.
The trick for the rest of us is reconciling the timing to what we think "Good Aikido People" are supposed to do. Sometimes we can be tempted to tie a late response to violence to a sense of morality informed by Hollywood fantasy. Only the bad guy moves first, the hero moves second. We say O Sensei wanted only a Defensive art, and equate that with delayed timing and waiting. For these people, taking the initiative is "Not Aikido."
That's not O Sensei's example.
Seeing me standing before him
My opponent cuts
But I am already behind him
