From this thread, it looks like you would have some amount of time at the least (probably hours?) I'm still looking for a more definitive answer since I would like to know as well.
Edit:
These two threads should be helpful.
It looks like it could be quite a while if you don't put it in water and keep it in a sealed container, even if you have opened it already. It should probably be looked into more just to be sure.
https://sanctioned-suicide.net/threads/sn-shelf-life-finding-please-help-other-members.13309/
https://sanctioned-suicide.net/threads/sn-shelf-life.3484/