Interesting example. When referring to an event that has duration -- that is not instantaneous -- such as dawn, normally "until" refers to the start of that event:

We will be frantically cleaning until the party.

Adding the "after" clarifies that the "until" refers to the end of that event:

We will be frantically cleaning until after the party.

In your example, what is being said is that the sun rising happens after dawn. (That is precisely correct: dawn ends when the first sliver of sun appears at the horizon.)

Interesting example. When referring to an event that has duration — that is not instantaneous — such as dawn, normally "until" refers to the start of that event:

We will be frantically cleaning until the party.

Adding the "after" clarifies that the "until" refers to the end of that event:

We will be frantically cleaning until after the party.

In your example, what is being said is that the sun rising happens after dawn. (That is precisely correct: dawn ends when the first sliver of sun appears at the horizon.)