Is there a time limit on the Hunger Games?

If a Hunger Games went on for too long - what would happen?

I was looking through the book for an answer and come across this quote:

In two weeks, 23 of you will be dead. One of you will be alive.

But, did Atala just say this as just a figure of speech, or was she was actually implying a time limit?

And it can't go on for ages or it would clash with the timing of the Victory Tour (this is taken place 6 months after each Hunger Games) and could possibly clash with the next Hunger Games too.

The gamemakers could kill off the victors and drive them together, but what would happen if this failed to work and they still didn't kill or attack each other.

Answer

No, there is no actual time limit. Further, the scene you reference from the movie does not happen in the book. From the first book's description of the Games (via Katniss, emphasis mine):

The twenty-four tributes will be imprisoned in a vast outdoor arena that could hold anything from a burning desert to a frozen wasteland. Over a period of several weeks, the competitors must fight to the death.

Later, as Katniss is thinking about the kind of environment she will find herself in:

Often there are trees because barren landscapes are dull and the Games resolve too quickly without them.

And, as Katniss and Peeta are holed up, she tries to figure out how long she has been away from home:

How long have I been gone? I'm guessing it's been about two weeks in the arena, and there was that week of preparation in the Capitol.

Lastly, as they are doing the "review show" at the end, it seems this particular games lasted "several weeks":

Condensing several weeks into three hours is quite a feat [...]

So, while I am unsure just how long the 74th Games lasted, there certainly was no two week time frame. We see several times that the Gamemakers will interfere to keep things interesting, so there is no reason to believe that they cannot essentially end it whenever they please.

Plus, they have been known to outright kill tributes in the past:

There was some speculation that the avalanche that finally took Titus out was specifically engineered to ensure the victor was not a lunatic.

Basically, they have (almost) complete control over the entire thing, including the duration.