How long to wait to test after PH adjusting?

I have been doing hydro for awhile but something has me thinking.
When you make a PH + or -, is there a amount of time one should wait before testing the soup?
I figure that other than for very small tanks, it would take a little time for the adjustment to equalize and become equal in the solution. My hot tub instructions for it say to add chemicals and test again in 24 hours.
If a hot tub says wait 24 hours to retest, how does that apply to a growing tank?
I have a 25 gal tank, and I make my adjustments and stir it up with a small pan and then test it.
Should I mix in my adjustments and then test it after X amount of time to be sure it is equally mixed in the soup? Or is mixing and testing right away good enough?

I have what I think are PH fluctuation issues and I wonder if I am chasing PH.

In my experences, when I adjust the ph and mix the soup for a minute or so thats all it takes. After 24 hours it will be different but it is always changing.

Thanks. I didn't think hydro would need a lot of time.

Good question, I was just thinking about this the other day. My 35 gal res takes about 5 mins for the ph to "stabilize" so to speak and become consistent.

I would think the larger the body of water the longer it takes. So yea, that makes sense.

What the water is doing is they key. If it has a lot of bubble action stirring it up, I think even a large res would fully dissipate pH up or down in one minute. That's how long I wait.