General Discussion

First, it doesn't make any sense because "Dawn is the time that marks the beginning of twilight before sunrise. It is recognized by the appearance of indirect sunlight being scattered in Earth's atmosphere, when the centre of the Sun's disc has reached 18° below the observer's horizon."

https://en.wikipedia.org/wiki/Dawn

Therefore, there is already sunlight scattering in the atmosphere before "dawn" so it isn't dark. Depending on the observer's location, the darkest time of night on a Moon-less night would probably be between 1:00 and 3:00 AM.

Still. the expression has a poetic quality.

Second, in the context of the post, there is a presumption of an outcome that is not guaranteed.