I prepare this solution myself once a year.I would not trust it fully after about 6 monthsbut then,you use it once to establish your processing procedureand your done with it.Don't spend your life testing;make some prints!(look who's talking)
This (IIRC) is a solution of Silver Nitrate in Acetic Acid. It should keep just about forever as long as it does not turn brown or form a precipitate in the bottle.