SilverFox
Hello Jeremy,
I haven't completed the testing on this, but under proper storage conditions water should be good for 5 years.
When you add sodium chlorite to water, the PH of the sodium chlorite is lowered and it begins the activation process. I have checked the level of chlorine dioxide after 6 months of storage, and it appears to be very similar to the initial amounts.
However, this testing is being done with closed containers. Things will be different with an open dish, but you should be good for a couple of days. If you mix up 3 liters and only go through 0.5 liters a day, store the unused solution in a cool place out of direct UV light and it should remain good until you use it up.
A good general rule to follow is that if you can't remember when you mixed the solution up, or have doubts about how you mixed it, throw it out and start over.
Tom