Crack of dawn and First blush

First blush and crack of dawn are semantically related in dawn topic. In some cases you can use "First blush" instead a noun phrase "Crack of dawn", when it comes to topics like first light, beginning of day, first part of the day.

First blush noun - At the first glimpse or impression.

Crack of dawn and first blush are semantically related in first glance topic. You can use "Crack of dawn" instead a noun phrase "First blush".