I can't give an exact time but probably safe for over 1 year but there are lot's of variables (HGH brand etc). The stuff they sometimes write on the label is nonsense though and the same for insulin. Insulin goes bad in 28 days
As I just posted in another thread I recently used expired insulin that I had first mixed over 1 year ago and it was fine. I have even used insulin (mixed) that wasn't kept in the fridge for a year and it was fine.
I have used an HGH vial I mixed 6 months prior and it still made me super tired so I know it was gtg. I am a good reference as most people use their HGH/peptide vials (so never find out) but I often start it and think fuck it and leave it for ages due to the side effects
Gonna start HGH soon at 1iu per day as last time even 2iu per day had my energy levels non existent after 1 week. I have also used MT2 and GHRP2 over 1 year after mixing and they were fine as well. MT2 is pretty much indestructible