With octopuses, it is especially important to check the water when you open the bag. If it is yellowish or brownish, speeding up the water matching process is desirable. If it is very cloudy, an immediate transfer to water adjusted as closely as possible but quickly is best. Fortunately, LA ships in lots of water and inking is usually not a problem. If you should need to move quickly, however, try to adjust a bucket of your tank water to the parameter of the shipping water by lowering/raising the salt content (I generally keep a bucket of super saturated saltwater handy for raising salt levels and fresh RO/DI will dilute and usually lower the PH).
If all is well and you notice no smell (testing for ammonia and nitrite are still a good idea though but your nose will also give you a clue if the water is fouled) then I recommend using which ever method you are comfortable with for shipped fish (I mentioned shipped because store bought do not usually have major PH differences). Place the bag in a bucket of tank water for temperature matching. Matching to your tank water can take from 1 to 3 hours depending upon the differences and your methods. I use a turkey baster but others prefer to drip. From LA there will be a lot of water and if the parameters are quite far apart (PH is usually the only major concern with LA), you will need to reduce quite a bit of the water to effect a change.
Watch for continued heavy breathing (over a 5 minute period) and/or total listlessness both are signs of stress and can be more lethal than acclimating too fast. If you note heavy breathing and the water is not polluted, try keeping out of sight, reducing the lights and offering a hiding place (shells, LR or macro algae work but any dark hidey hole is usuall accepted). If it continues, you can add air from an air pump but keep the bubbles away from the mantle. If this does not help, speed up your acclimation to get it into a quiet, dark tank.
If you have a critter keeper or other drainable container, placing this in the bag and encouraging the animal into it will make transfering to the aquarium easier (shells will work for this too).
When you place it into the aquarium, let it leave the container on its own. This species usually exits to the live rock within a minute or two. Lowering or turning off your lights for the first day is often recommended to reduce stress. I don't often adhere to this unless I sense a problem but it is definitely not harmful.
DO NOT leave the open container unobserved. I have several acclimation photos showing WHY this is not a good idea but, as you might imagine, they CAN crawl up the side of the bag and exit.
Thanks i did just as you said except I didn't use a container for him i let him go straight into the tank his breathing is normal and it is a he. He has hidden in this little cave and has eaten one possibly two hermit crabs. He has been exploring the back of the tank and peering out at me as i come by.