Rush, as then, perhaps (6)
I believe the answer is:
hasten
'rush' is the definition.
('hasten' can be a synonym of 'rush')
'as then perhaps' is the wordplay.
'perhaps' indicates anagramming the letters.
'as'+'then'='asthen'
'asthen' with letters rearranged gives 'HASTEN'.
(Other definitions for hasten that I've seen before include "Act or move fast" , "Rush" , "Be quick to do something" , "Make faster" , "race? - with 26a" .)