Okay, And you said to have the tank have 2.0ppm of Copper before adding him or ramp it up to that after adding it, and then start the day once it passes 2.0?Tangs take copper well. The problems are if they are already sick before you get them. It's not the copper that's killing them it's what ever issue they are fighting at the same time as the heavy stress from transportation has already weakened them. If you skip it and they do have something, next time they get stressed it more than likely will return and could spread to other fish at that point and you get an outbreak.
It's better to take the risk now and treat them for at minimum 14 days and then into an observation tank for another 14 days. Better off doing 30 days at 2.3ppm coppwe power. Start at 2.0 and ramp up to 2.3-2.5.
I use sandbeds in my qts now. After I found it does not absorb copper well but will still give bio filtration benefits. Sandbeds also help the fish feel more comfortable it seems. The bio filtration helps them a lot. Get pool filter sand from Ace or Home Depot and use that for your sand. It's real cheap and makes it affordable to toss at the end of the 30 day qt. Or you can sterilize the sand in between qt tanks which is what I do.
But for Tangs, if you don't prophalticly treat any other meds like prazi for flukes do the copper for the 14 days. They cary these parasites so easily and can have them and not be symptomatic until they get stressed.