Start of May, end of three months for elected representative (6)
I believe the answer is:
member
'elected representative' is the definition.
(eg Member of Parliament)
'start of may end of three months' is the wordplay.
'start of' says to take the initial letters.
'end of three months' becomes 'ember' (September, November and December).
The initial letter of 'may' is 'm'.
'm'+'ember'='MEMBER'
'for' acts as a link.
(Other definitions for member that I've seen before include "One belonging to a club" , "Limb - element - one in society" , "constituent" , "One who has joined, eg, a society" , "Person belonging to a particular club or society" .)