As soon as clocked in the workplace can be heard (2,5)
I believe the answer is:
on sight
'as soon as clocked' is the definition.
('clock' can mean to see or notice)
'in the workplace can be heard' is the wordplay.
'in the workplace' becomes 'on site' (on site can mean at an official workplace).
'can be heard' shows a homophone (sound like).
'onsite' is a homophone of 'ON SIGHT'.
(Other definitions for on sight that I've seen before include "without a second glance?" , "Without rehearsal performing" , "How to shoot dangerous criminal" , "at time of presentation" , "when observed" .)