Power failure resulting from them not being in on time (6)
I believe the answer is:
outage
'power failure' is the definition.
(I've seen this in another clue)
'not being in on time' is the wordplay.
'not being in' becomes 'out' ('out' is the opposite to 'in').
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'time' becomes 'age' (an age is a period of time).
'out'+'age'='OUTAGE'
'resulting from them' is the link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for outage that I've seen before include "Emaciated" , "time of no power" , "Temporary suspension of operation" , "loss of power" , "When one lacks power" .)