A black time is a terrible thing (5)

I believe the answer is:

night

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'a black' is the definition.
(night can mean as black as night)

'time is a terrible thing' is the wordplay.
'thing' anagrams to 'NIGHT'.
Though, I'm not clear how this is indicated.

Can you help me to learn more?

(Other definitions for night that I've seen before include "Dark hours" , "Evening" , "See 1 Across" , "period of gloom" , "Hours of darkness" .)

I've seen this clue in the Evening Standard.

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