If you are registering 0 chlorine this morning, you don't want to wait until evening to add bleach. Go ahead and add it now if you don't want your pool to turn green!

A pool store should have an OTO kit. Just don't let them talk you into buying anything else while you are there. They will try! But, even after you do get a cheap OTO kit, you still should order a K2006. That kit will not be available locally and you will have to order it. (Link in PoolDoc's post above.) If your pool store happens to have a K2005 don't buy it. Not the same thing and not what you want.