Extremely unpunctual date came around at last (8)

I believe the answer is:

ultimate

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'at last' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

(Other definitions for ultimate that I've seen before include "Final - mutilate (anag)" , "Best - last" , "Happening last" , "The last element of a series" , "Last or highest" .)

I've seen this clue in the Sydney Morning Herald.

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