If you wash thoroughly and then tone, I beleve the working solution will not degrade at all.
I have a 1+9 stock that all fine quality FB prints get stabilized toned with. It lives in a dark glass bottle, typically in my dark cool basement darkroom .
I ocassionally 'replenish' it. I somewhere found the rated capacity of the 1:9. Likely an old Kodak darkroom datagude.
So after about 5 or 6 8x10's I add some full strength KRST, x ml per print processed. .
I don't recall the quantity - I have it written on the bottle, which is not close at hand.
This same solution has been on the go for over 7 years now.