How long to use a vial.

My friend is stopping Tirz and she is selling her remaining vials to another friend. They are just starting out and going to follow the titration schedule. The vials are all 72mg. Is it more about the time from being opened/first poked? Or more about how many times a vial has been poked? I’m trying to help him figure out safety, the real issue, and how to minimize loss of medication. Any information is welcome 🙏🏼