Alarm, just after five, yours truly’s switched off (6)
I believe the answer is:
fright
'alarm' is the definition.
(both can mean fear or worry)
'just after five yours truly's switched off' is the wordplay.
'just' becomes 'right' (similar in meaning).
'after' is a charade indicator (letters next to each other).
'yours truly's' becomes 'I've' (yours truly has, I have).
'switched off' indicates named letters should be taken away.
'five' with 'ive' taken out is 'f'.
'right' after 'f' is 'FRIGHT'.
(Other definitions for fright that I've seen before include "Grotesque" , "Start" , "Sudden feeling of fear" , "A scare or shock" , "Sudden exposure to fear" .)