Both Uses

opportune
in
Story of My Life
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He was a famous story-teller; after I had acquired language he used to spell clumsily into my hand his cleverest anecdotes, and nothing pleased him more than to have me repeat them at an opportune moment.†
Chpt 2 *
I suppose the calls of the stupid and curious, especially of newspaper reporters, are always inopportune.†
Chpt 23

inopportune = bad circumstances for a particular purpose -- especially the circumstance of timing

standard prefix: The prefix "in-" in inopportune means not and reverses the meaning of opportune. This is the same pattern you see in words like invisible, incomplete, and insecure.

Definitions:

(1) (opportune)
favorable circumstances for a particular purpose -- especially the circumstance of good timing
(2) (meaning too rare to warrant focus)