Actually, I can't get RA-4 working solution go bad even if I try! I had some 1,5 years old, heavily used, lying around (in a squeezed bottle) and it worked just fine. I have left the developer in open trays for several days in some occasions, and it still works. I just find it more robust than any other color or BW process or BW paper developers.
Of course, this doesn't mean that you have to try to abuse it like I did . But this should give you some idea about the "safety margin".