Not quite second, coming in last, somehow (6)
I believe the answer is:
almost
'not quite' is the definition.
(I've seen this before)
'second coming in last somehow' is the wordplay.
'second' becomes 'mo' (both are short periods of time).
'coming in' is an insertion indicator.
'somehow' indicates anagramming the letters.
'last' with letters rearranged gives 'alst'.
'mo' going into 'alst' is 'ALMOST'.
(Other definitions for almost that I've seen before include "Not totally" , "practically" , "Nearly, not quite" , "Slightly short of" , "As good as" .)