The most common and most likely answer to this crossword clue is the 7 letter word DIURNAL
I've seen this crossword clue in Financial Times
D
I
U
R
N
A
L
More clues leading to the result DIURNAL
- Seemingly relaxed about vessel active by day
- Call about vessel during the day
- Ring about vessel moving about in daylight
- Face closing supplier of tea that is open during the day
- Face carrying pot daily
- Phone about vase during the day
- Call about run to work out daily
- Run frantically in ring for a day
- Laid back guards reportedly get income daily
- Vase stored in pan for the day
Buddy explains!

The straight part
We know that "during the day" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case during the day = diurnal.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.
What does DIURNAL mean?
DIURNAL noun- A flower that opens only in the day.
- A book containing canonical offices performed during the day, hence not matins.
- A diary or journal.
- A daily news publication.
- Happening or occurring during daylight, or primarily active during that time.
- Said of a flower open, or releasing its perfume during daylight hours, but not at night.
- Having a daily cycle that is completed every 24 hours, usually referring to tasks, processes, tides, or sunrise to sunset; circadian.
- Done once every day; daily, quotidian.
- Published daily.