I try to use it all up within about 8 weeks. Anything longer and I'll split it and freeze half. Nothing I use is super sensitive except the GHK-CU in KLOW, but my biggest vials of that are 6 weeks anyway.
My thinking is this: I'm not young, I filter everything, my sterile technique is pretty good, and I almost never get sick and heal quickly. If I wasn't any of those things, I'd aim for a shorter time.