Occurrence I’d expected at first? It’s late in the day (8)
I believe the answer is:
'late in the day' is the definition.
(I've seen this before)
'occurrence i'd expected at first?' is the wordplay.
'occurrence' becomes 'event' (I've seen this before**).
'at first?' suggests taking the first letters (I've seen 'at first' mean this).
The first letter of 'expected' is 'e'.
'it's' acts as a link.
(Other definitions for eventide that I've seen before include "latter part of the day" , "End of the day (poetic)" , "End of the day to the poet" , "onset of dusk" , "The day's close (poetic)" .)