Shelf life is not a major issue. Running 1 cycle of the generator will produce a strength of liquid that typically lasts 2 weeks. The shelf-life can be increased with running more than 1 cycle.
A batch of solution can also be re-run through the generator at any time to make sure it is at full strength. What’s important is that you have unlimited access to a sanitizing solution that’s easy to make on your own using only two ingredients: salt and water.