Shrewd signal saving time (4)
I believe the answer is:
cute
'shrewd' is the definition.
(I've seen this before)
'signal saving time' is the wordplay.
'signal' becomes 'cue' (as in an actor's cue).
'saving' indicates putting letters inside.
'time' becomes 't' (abbreviation).
'cue' placed around 't' is 'CUTE'.
(Other definitions for cute that I've seen before include "Fly" , "Sweet, attractive" , "Charming, quaint" , "Daintily pleasing" , "Location" .)