The most common and most likely answer to this crossword clue is the 11 letter word ANACHRONISM
I've seen this crossword clue in The Daily Telegraph
A
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More clues leading to the result ANACHRONISM
Buddy explains!

The straight part
We know that "untimely error" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case untimely error = anachronism.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 ANACHRONISM mean?
ANACHRONISM noun- A chronological mistake; the erroneous dating of an event, circumstance, or object.
- A person or thing which seems to belong to a different time or period of time.