Extra seconds showing manners (5)
I believe the answer is:
mores
'manners' is the definition.
(I've seen this in another clue)
'extra seconds' is the wordplay.
'extra' becomes 'more' (both can mean additional).
'seconds' becomes 's' (abbreviation).
'more'+'s'='MORES'
'showing' is the link.
(Other definitions for mores that I've seen before include "Customs, manners" , "Customs and conventions of a community" , "of St Thomas's" , "(Society's) conventions" , "O tempora, O - !" .)