If I die, sadly, start to sob after sun sets (10)

I believe the answer is:

solidifies

'sets' is the definition.
(to solidify is to harden or set)

'if i die sadly start to sob after sun' is the wordplay.
'sadly' indicates an anagram.
'start to' suggests taking the first letters.
'after' means one lot of letters go next to another.
'sun' becomes 'sol' (Latin for 'sun').
The initial letter of 'sob' is 's'.
'if'+'i'+'die'='ifidie'
'ifidie' anagrammed gives 'idifie'.
'idifie'+'s'='idifies'
'idifies' after 'sol' is 'SOLIDIFIES'.

I've seen this clue in The Times.

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