how long does it take to go back to optimal performance?

 

about 0 seconds, give or take 0 seconds

 

I thought I remember reading that when a knock sensor goes bad, its instant, but when going back to normal it doesnt..

 

No, many sensors on our car have a 2 trip memory thingy. Like if you take out a certain evap component and drove your car for 10k miles without ever turning off the car you wouldn't get a code. Now, take out that same component and go for a 5 minute drive, stop and turn off the engine, turn it back on and the CEL will be on. The KS isn't one of these, it goes back to normal almost instantly.

 

Should I reset the ECU right after I install my knock?

 

im guessing that would be an affirmative