Hey Bro,
It should only be re-constituted right before it's used. With that being said most HGH is in 10iu vials; unless you're taking an extremely low dose that shouldn't stick around for very long. And at that short of time you should be okay. 10iu's in my house would be gone in a few days.
humatrope says to only leave it 30 min out of the fridge max, but i've also read from gh therapy clinics saying that 24 hours out the fridge is the max