Crossword Genius

One drug in prison in time for chilling? (3,3)

Ross

I believe the answer is:

ice age

I'm a little stuck... Click here to teach me more about this clue!

'time for chilling?' is the definition.
The definition and answer can be both related to time as well as being singular nouns.
Perhaps they are linked in a way I don't understand?

'one drug in prison' is the wordplay.
'one' becomes 'i' (Roman numeral).
'drug' becomes 'e' (E is another name for ecstasy).
'in' means one lot of letters goes inside another.
'prison' becomes 'cage' (cage is a kind of prison).
'e' placed inside 'cage' is 'ceage'.
'i'+'ceage'='ICE AGE'

'in' acts as a link.

Can you help me to learn more?

(Other definitions for ice age that I've seen before include "When glaciers covered a large part of the earth's surface" , "Cold spell (a very long one!)" , "Period of extreme cold" , "Cold period for Earth" , "when it gets very cold" .)

I've seen this clue in The Times.
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