if the 2nd party isn't online when a hedgehog channel is created where is the information about state changes stored
State changes need to be sent by the 1st party to the 2nd party through some text medium like email. Whatever medium you use is where the information is stored.
how can party 2 access it once it comes online?
They check their email or telegram or whatever you used to send them the new state
Thank you for the great work you've been doing!
You're welcome! :D