Ted:(posted 8372 days ago)Indefinitely - as many times as you open and shut the bottles. The only difference will be a miniscule difference in concentration if the humidity is different each time you open it-the difference being in parts per million.
If you took a bottle of 10% NaOH (Sodium Hydroxide) and placed it beside a standard silver print, the print would fade (100 yrs) before the NaOH would change. It may dissolve a bit of the glass bottle, but it would not deteriorate. Of all the photochemicals used, it is most likley the least affected by time or oxygen.
Yours chemically.
Richard