Well I meant the longevity of the image formed, but that's good to know. Thing is, though, either usually comes together (or did in the old days, I guess now for stuff like Kodak it's big quantities of each solution) in a kit, and however unstable a bleach-fix may be, developer was more so. I mixed enough for one session and used it all one shot so it didn't much matter how long it lasted at working solution. In concentrate form I mostly used it up before it went bad and, if I didn't, it was the developer that seemed to die.
The big issue now though is that only the kits with combined bleach-fix (oh, ok, "blix") are conveniently available in reasonable sizes (excluding the Flexicolor kit for C41 from PF, but that's also quite expensive compared to the alternatives.)