In elevated post, it’s late in the day to tuck into some breakfast (7)
I believe the answer is:
topmast
'in elevated post' is the definition.
'topmast' can be an answer for 'post' (I have seen 'high post' mean 'topmast' so perhaps 'post' could also mean 'topmast'). I'm unsure of the 'in elevated' bit.
'it's late in the day to tuck into some breakfast' is the wordplay.
'it's late in the day' becomes 'pm'.
'to tuck into' means one lot of letters goes inside another.
'some breakfast' becomes 'toast' (I've seen this before).
'pm' inserted within 'toast' is 'TOPMAST'.
(Other definitions for topmast that I've seen before include "High part of sailing ship" , "high post" , "post on board" , "Most apt (anag) - feature of a square-rigged ship" , "Part of square-rigged ship" .)