To pass the time, electronic engineers start with circuits inside. (6)
I believe the answer is:
elapse
'to pass' is the definition.
('elapse' can be a synonym of 'pass')
'electronic engineers start with circuits inside' is the wordplay.
'start with' indicates taking the first letters.
'circuits' becomes 'laps' ('lap' can be a synonym of 'circuit').
'inside' is an insertion indicator.
The initial letters of 'electronic engineers' is 'ee'.
'ee' enclosing 'laps' is 'ELAPSE'.
'the time' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for elapse that I've seen before include "Of time, pass by - please" , "Go past" , "'Pass by, as time (6)'" , "Slip away" , "run by" .)