Briefly watch fashions: they’re often imitated (4,6)
I believe the answer is:
role models
'they're often imitated' is the definition.
(people imitate role models' behaviour)
'briefly watch fashions' is the wordplay.
'briefly' means to remove the last letter.
'watch' becomes 'Rolex' (Rolex is a watch manufacturer).
'fashions' becomes 'models' (both can mean to make or shape).
'rolex' with its last letter taken off is 'role'.
'role'+'models'='ROLE MODELS'
(Other definitions for role models that I've seen before include "ideals" , "People, celebrities, worthy of imitation" .)