So when it's in powder state you can keep in the temperature room ?
It's supposed to be different depending on brand. Different preservatives and what not.
The times given in the package inserts are the time frames it's guaranteed fully potent. Sometimes these times are minimized by the manufacturer to make more money - patient thinks he needs to throw away his GH and mix a fresh amp. Kind of like the expiry dates on all other meds, whether tablets or oily injectable solutions, etc. Many drugs are fully potent much longer and the manufacturers know it. Expired drugs are often sent to Africa as foreign aid.

So the answer is that it's hard to know for sure.