Interesting question.
In addition to waiting, what other variables to you try to control to make sure you’re hearing a change only in the element of the system which has been altered?
Typically, these other variables might include time of day, mood, music selection, furniture and/or treatments, other things using electricity in the house, and more. If tubes are used in the system, this can be a challenge, as tubes which are a month or two older will introduce changes of their own. One would have to swap in identical tubes with close to the same amount of wear to control that variable. (Personally, I try to keep tubes out of the equation when I listen for changes.)
Curious what else you try to keep stable.