So what constitutes the end of the opening and the start of the middle game?

I was looking at a post by Billium where he was asking what is the longest opening ever accomplished here on cess.com and someone made mention of the idea that his example was "clearly" into the middle game.  So my question is what actually signals the end of the opening?  I understand Billium's point that he's considering all of the moves with all of the variations as an opening is this correct thinking?

nothing:)

For popular lines, as soon as you are out of book, you are in the middle game.

I read in a book once that you have reached the middlegame once you start looking where best to deploy your rooks and I think that , in general, this is the best definition I have seen as to when the middlegame is entered and the opening finished. Ofcourse there is no hard and fast rule that wont have exceptions. You can be out of book and still be in the opening and still be in book and be in a middlegame. Many openings now are analyzed well into the middlegames of that particular opening.

Some (slightly contentious) definitions here.

For the endgame, I've read somewhere that it is when both you and your opponent have two pieces or less left, regardless of how many pawns there are.

Just listen for the chime.

Ah, parting is such sweet sorrow.  Don't we hear the chimes at midnight?