It's distrubing that her fingers seem to be in her mouth - kind of looks like she's going to bite them. Other than that, good composition and fits the challenge well.
The picture's too tilted (needs to be rotated slightly to the right) and the restroom's sign is askewed too. But I love the young models' acting (I'm assuming this was arranged), wish I can see the white-shirted model's face. Good idea in making this black and white. The picture gave me a chuckle when I saw it. Way to go!
The image doesn't sell "waiting" very strongly. Posing the subjects leaning against the wall would strengthen the message. The yawn looks a bit off, and there's too much wall above the yawner. While the execution has small flaws, the concept is sound.