It all depends, TAR has done several two hour blocks that were 2 separate episodes shown back to back. Most of the 2 hour final episode were in fact two separate episodes just shown on the same night (or as a poster mentioned the two Germany episodes of All Stars).
But the 2 hour openers (so far) have all been one episode that has been edited as a two hour episode instead of a single one hour episode.
At this stage I don't know which I think it is. I know I am hoping that its the single episode shown over two hours.
I would naturally assume (based on TAR rating strength in comparison to the rest of its sunday lineup) that it is one episode, just shown over 2 hours. HTe main reason I think this...
Its a huge way to get 2 hours at very little additional cost. And since CBS has had some significant financial problems its a great way to fill an hour and save al ot of cash.
As an example, if a leg of TAR cost the production 1 million (just picking a number, I have no idea). Then those are the set cost. Thats covers all the preproduction, all the actual location filming and travel expense, and all the post production cost (editing, score, voice over work).
By stretching the film material into two hours (which was done in seasons 5, 6, 7, 8, and 9) they incur no additional preproduction cost, and most importantly no additional filming and travel costs (the largest part of TAR's budget).