The most common and most likely answer to this crossword clue is the 8 letter word LACKADAY
I've seen this crossword clue in The Times
L
A
C
K
A
D
A
Y
More clues leading to the result LACKADAY
Buddy explains!

The straight part
We know that "Not be able to arrange a date, alas" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case not be able to arrange a date, alas = lackaday.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 LACKADAY mean?
LACKADAY interjection- An expression of regret or grief.