What you should do is add your tank water to the bag a little at a time, maybe over 1/2 hour. It's been floating for some time, so the temperatures must be about equal. Then pick up your little octo and put him in the water - don't empty the water into the tank, if you can help it.
well i took the other one back and the guy said i could have the last one they had and gave him to me. i floated him for 20 mins then drip aclimated him and had the lights out for a few hours and came back and he was out climbin around doin great. i put some crabs in there and have been waiting to come out :D . im gonna name him Gus