As Reefkeeperz said it is effective but also toxic and should be used as a last resort. Some fish do not tolerate copper treatment and are to sensitive like many tangs. The TTM is very effective and less stressful for the fish but a little more involved. This is a very detailed comprehensive write on the tank transfer method. http://reefcentral.com/forums/showthread.php?t=2388428 Depending the size of the fish you are treating it can be as simple as 2 5g buckets but with tangs you will likely need something bigger.
To nit pick a bit, copper treats WAY more than TTM ever could hope to. OP, I would recommend looking into Cloroquine phosphate. It can treat a wide range of what ails our fish, and is safer than coppper. Some wrasses are sensitive to it though.
Ich can complete its life cycle in as soon as about a week, or it can take as long as 70-some days. It depends on how long it stays in its encysted from. I believe the average is about a couple weeks. The longer you wait, the more certain you can be.
TTM takes 12 days. You can use your display water if you are absolutely sure that it is sterile (as far as ich).