I think everyone's experience will vary, so let's just make sure we test our water parameters periodically to make sure it's usable either immediately or after "aging" for an extended period of time.
For me, I can use the same water both days, I just need to set my expectations. If I uses immediately, my pH may be higher, as will Alk and CA. If I let it sit, it's definitely still usable, I just need to adjust the parameters to my liking.
I've started "cutting" my aquavitro with normal IO, to cut costs and also to help with the clouding of the aquavitro. As I mentioned, aquavitro can supposedly be used immediately, but according to the IO site, it says "Always allow newly mixed salt water to circulate with a powerhead or airstone at least overnight before use." We'll see how it goes.