Typically taking a very short time (2,7)
I believe the answer is:
on average
'typically' is the definition.
(I've seen this in another clue)
'taking a very short time' is the wordplay.
'taking' becomes 'on' (eg one taking drugs is 'on' drugs).
'a very short time' becomes 'average' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'on'+'average'='ON AVERAGE'
(Other definitions for on average that I've seen before include "Generally" , "Usually" , "typically speaking" .)