Board express to save time (4)
I believe the answer is:
stay
'board' is the definition.
(I've seen this before)
'express to save time' is the wordplay.
'express' becomes 'say' (I've seen this before).
'to save' is an insertion indicator.
'time' becomes 't'.
'say' placed around 't' is 'STAY'.
(Other definitions for stay that I've seen before include "Corset strut" , "guy giving > support" , "Abide" , "Defer" , "Supporting rod" .)