to find the answer to what opening is the longest you must first find the answer to where does openings stop and middlegames begin since there is no clear definition to that. good luck with that one:)
Actually, to my question there is a very clear definition. If it is listed in Chess.com's database of opening positions, it counts. If it's not, it doesn't. Which Opening Position starts the furthest into the game?
the definition was not clear at all. you just said that the opening had to be available at chess.com not chess.com exlusive, so i thought that was because you wanted to use chess.com to help study the opening you end up choosing in addition to learning the ideas and plans and the theory from sources more fit for this. i assumed you asked because you wanted an opening complicated or something because it would never have crossed my mind that you prefer handicapping yourself with wanting chess.com database exlusive 
i think i answered the original question clearly
by the way this is no bashing of chess.com database which is good. there is just no reason to only have one source
Right! If I understand correctly, the question is asking; which of the chess.com presets will start a game furthest into the game; whether you concider it the opening or middlegame or endgame is irrelevent.
Only Billium248 can give me the answer which I seek.
Yow Batman!