The most common and most likely answer to this crossword clue is the 3 plus 3 letter word ALL DAY
I've seen this crossword clue in The Guardian
A
L
L
D
A
Y
More clues leading to the result ALL DAY
Buddy explains!

The straight part
We know that "from dawn to dusk/from dawn to dusk" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case from dawn to dusk/from dawn to dusk = all day.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
Crossword Answer definitions
ALL DAY adjective- Lasting throughout the whole day.
- Available throughout the whole day.