Time of disturbance moved forward for small group (4)
I believe the answer is:
trio
'for small group' is the definition.
(I've seen this before)
'time of disturbance' is the wordplay.
'time' becomes 't' (abbreviation).
'of disturbance' becomes 'rio' (I am not sure about this - if you are sure you should believe this answer much more).
't'+'rio'='TRIO'
'moved forward' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
(Other definitions for trio that I've seen before include "Beethoven's 'Archduke': famous piece written for this ensemble" , "Archduke, possibly" , "Band of three" , "Musical group" , "Three of a kind" .)