Synchronised, however (2,3,4,4)
I believe the answer is:
at the same time
I believe this clue is a double definition.
'synchronised' is the first definition.
(I've seen this before)
'however' is the second definition.
(I've seen this before)
(Other definitions for at the same time that I've seen before include "synchronised" , "nonetheless" , "Notwithstanding" , "on the other hand" , "Coincidentally - still - however" .)