The most common and most likely answer to this crossword clue is the 4 plus 4 plus 8 letter word ZERO HOUR CONTRACT
I've seen this crossword clue in The Guardian
Z
E
R
O
H
O
U
R
C
O
N
T
R
A
C
T
Buddy explains!
The straight part
We know that "Variable working horror — cue to act over numbers initially on it?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case variable working horror — cue to act over numbers initially on it? = zero hour contract.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.