The official listed shelf life is 6 months in a full stoppered bottle. This assumes dark storage.(posted 8388 days ago)Using marbles or nitrogen air replacements will help, but once you open the bottle and pour some out, degradation will start on the remainder of the bottle, so even with these measures, you will have reduced lifetime if you are using solution over time.
For best results, use glass bottles. Most plastic bottles will allow a small amount of oxygen to penetrate.
David Carper ILFORD Technical Service