Can i answer both? I consider stable alk when it is about the same if measure at the same time everyday.
Ideally i would love to have it stable through the whole day and dose at just the right time to keep it perfect. That is not realistic unless you have something like kh director(or similar automated testers/dosers). Eventually i will get one though.
Having said that though i also try to add more stability to my PH and also keep it higher. Because of this i focus my alk dosing more overnight through early afternoon so my alk is probably highest in the morning hours. It helps to keep my ph in a tighter day/night range though.
So neither my alk or PH end up perfectly stable, but it is a fairly small range for both.