In agreement lasting sixty seconds, dissent’s beginning (2,3,4)
I believe the answer is:
of one mind
'in agreement' is the definition.
(I've seen this before)
'lasting sixty seconds dissent's beginning' is the wordplay.
'lasting sixty seconds' becomes 'of one min' (1 minute).
'beginning' suggests taking the first letters.
The initial letter of 'dissents' is 'd'.
'ofonemin'+'d'='OF ONE MIND'
(Other definitions for of one mind that I've seen before include "Sharing an opinion" , "Agreed" , "In agreement" , "Unanimous" , "In accord" .)