You mean StarSan (sanitizer)?
A working solution should remain active as long as the pH is under 3.0 (a pH of 2.7 is the target I think).
The instructions also say that it should be discarded when it gets cloudy, but that's not always true. As long as you're using soft or RO water to mix it, it seems to work just as fine when it gets a bit cloudy, at least in my experience.
I've kept (cloudy/hazy) working solutions for weeks, months even. They get crystal clear after a few months, leaving a white residue on the bottom of the bucket and all over the stuff that's in there. It washes or brushes off easily.
You can soak things in there for much longer than the 1 minute minimum contact time per their directions.
Except for mesh bags or so it won't sanitize much better or more thoroughly, but a 10-30 minutes soak is A-OK. Hours, days, weeks, months even, seem to be alright. Transparent plastics, such as vinyl tubing, may become hazy, milky, or even opaque after a few days to weeks. They'll become transparent again after they dry thoroughly.
Some materials will dissolve in it, it's an acid after all. So copper, brass, aluminum, etc. and anything else that get attacked by acids, should not be kept under Starsan for longer times. It can make your copper immersion chiller bright and looking like new with a few hour soak. Same for brass fittings.
Stainless gets a nice shine too with longer soaks (weeks, months).