I would recommend using or freezing oysters within a day of purchasing them.
It depends on whether the oysters are shucked, or live. Shucked oysters can be refrigerated for 1-2 day, and frozen for 3-6 months.
Live oysters can be refrigerated for 2-3 days, and kept frozen for 2-3 months.
If the Oyster are Fresh They are best kept wrapped in a damp cloth in the fridge. To tell if the Oysters are Dead (In te Shell) is the same as with Mussels.. If they are tightly shut they are ok! If they are open pick it up after a few squeezes They will slowly tightly shut if not they are "Talking" therefore they are dead and poisonous!!
To the trained nose and eye you can tell if the shucked oyster is Off or Dead. The oyster can also give off an "Off" odour/ milky complexion during breeding season. I personally wouldnt eat an oyster unless i watched as it was shucked in front of me!
Other people asked questions on various topics, and are still waiting for answer. Would be great if you can take a sec and answer them