The most common and most likely answer to this crossword clue is the 9 letter word TIMESCALE
T
I
M
E
S
C
A
L
E
Buddy explains!
The straight part
We know that "‘Estimated period to complete work" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case ‘estimated period to complete work = timescale.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 TIMESCALE mean?
TIMESCALE noun- A series of events used as a rough measure of duration.