They're instrumental in an early response (5)

I believe the answer is:

lyres

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'they're instrumental' is the definition.
The definition suggests an adverb but the answer is not.

'in an early response' is the wordplay.
'in' indicates a hidden word.
'LYRES' is hidden within 'early response'.

Can you help me to learn more?

(Another definition for lyres that I've seen is " Ancient Greek harps".)

I've seen this clue in the Evening Standard.

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