Twelve men onto one, somehow (8)
I believe the answer is:
noontime
'twelve' is the definition.
(I've seen this in another clue)
'men onto one somehow' is the wordplay.
'one' becomes 'i' (Roman numeral).
'somehow' is an anagram indicator.
'men'+'onto'+'i'='menontoi'
'menontoi' with letters rearranged gives 'NOONTIME'.
(Other definitions for noontime that I've seen before include "Around midday" , "around 12" , "Middle of the day" .)