I want to put in a 44" x 12" shelf in our tiny dining room that can be used as a temporary buffet and then folded down against the wall when not in use. I'm planning to use those folding shelf brackets that click into place when the shelf is 90 degrees, and then touch a lever that collapses them to fold down. I'm ordering a very pretty piece of finished maple that will look good hanging on the wall. Should I have the brackets installed on the wood first, or do they need to be installed on the wall first? One bracket reviewer on Amazon said that they have to be attached to the wall first, "plumb to the floor" or they won't work. Is that true? It would be easier for me if I could have the brackets already attached to the shelf when I get it.