When one was poor and didn't have to slim? (4,5)

I believe the answer is:

lean years

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'when one was poor' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.

'didn't have to slim?' is the wordplay.
'didn't have' becomes 'years' (I can't justify this - if you can you should believe this answer much more).
'to' is a charade indicator (letters next to each other) (I've seen this in other clues).
'slim?' becomes 'lean' ('lean' can be similar in meaning to 'slim').
'years' after 'lean' is 'LEAN YEARS'.

'and' is the link.

Can you help me to learn more?

I've seen this clue in the Evening Standard.

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