Obviously not a soft time (4,3)

I believe the answer is:

hard day

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'obviously not a' is the definition.
I don't know anything about this answer so I cannot tell whether this works.

'soft time' is the wordplay.
'soft' becomes 'hard' (I can't explain this - if you can you should give a lot more credence to this answer).
'time' becomes 'day' (day is a kind of time).
'hard'+'day'='HARD DAY'

Can you help me to learn more?

I've seen this clue in the Evening Standard.

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