Hey! Public transport takes two seconds! (4)
I believe the answer is:
psst
'hey' is the definition.
Both the answer and definition are interjections.
Perhaps they are linked in a way I don't understand?
'public transport takes two seconds' is the wordplay.
'public transport' becomes 'pt' (this might be a standard abbreviation of which I'm unaware).
'takes' is an insertion indicator.
'two seconds' becomes 'ss' (abbreviation for second times two).
'pt' going around 'ss' is 'PSST'.
Can you help me to learn more?
(Other definitions for psst that I've seen before include "It's said to draw attention" , "Notice me" , "Sibilant sound made to attract attention" , "Sound used to attract someone's attention" , "Surreptitious attention-seeker" .)