The most common and most likely answer to this crossword clue is the 10 letter word OUTPATIENT
I've seen this crossword clue in Financial Times
O
U
T
P
A
T
I
E
N
T
Buddy explains!
The straight part
We know that "Overnight case? No" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case overnight case? no = outpatient.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 OUTPATIENT mean?
OUTPATIENT noun- A patient who receives treatment at a hospital or clinic but is not admitted overnight; a receiver of ambulatory care.
- Provided without requiring an overnight stay by the patient.