They last only the time directly after the noise is made, there is never an extended time in which they occur. As for a pattern I do not see one at all, they are directly triggered by rapid noises around him, especially sharp rapid noises, but even the crumple of a piece of paper can trigger them.
All of my cat's behaviors have been completely normal, the only thing that is varied is the violent twitching. He is still responsive to me, food, and has had no bathroom issues. He is 16 and the vet said he wishes some kittens had the blood that he has... all is normal according to the vet
I have taken a video of my cat while having an "attack". At first these violent twitches only occurred when I made a sharp rapid noise such as a kiss* noise or a ding ding ding with a spoon on a bowl. Now just at random times he will have these violent twitches that sometimes even make him lose...