Trespasser in time more discourteous (8)

I believe the answer is:

intruder

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'trespasser' is the definition.
(I know that trespasser can be written as intruder)

'in time more discourteous' is the wordplay.
'time' becomes 't' (abbreviation).
'more discourteous' becomes 'ruder' (I can't justify this - if you can you should give a lot more credence to this answer).
'in'+'t'+'ruder'='INTRUDER'

Can you help me to learn more?

(Other definitions for intruder that I've seen before include "One entering uninvited" , "Gatecrasher" , "Housebreaker" , "I'd return (anag.)" , "One entering unasked" .)

I've seen this clue in The Sun.

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