Maybe you're hasty in saying you haven't got it (3,3)

I believe the answer is:

all day

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'got it' is the definition.
The answer and definition are different parts of speech. However, adjectives and past participle verbs sometimes define each other.

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for all day that I've seen before include "morning and afternoon" , "until even" , "From dawn to dusk" .)

I've seen this clue in the Evening Standard.

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