I would think there would be some instructions on the cardboard that the tether was attached to.
I don't know if it is freezer safe but I would think so.
I would think you can leave it in the refrigerator or freezer (if it can go there) as long as you want. You would want to leave it in at least several hours for it to cool to the correct temperature.
I've got those teether.
I think you put them in the fridge for a bit for them to cool. once cool take them out and chew on them.
they are designed to stay cool for a while.
you can still use them without cooling them.
I have one of those they're really nice.
I've heard freezing them too long may cause them to pop so be careful with that. Also don't boil it. Ever.
Personally, I put them in the freezer for 30 min to an hour. But I like mine really cold.
If you want to be safe, leave them in the fridge.