Runs away at bedtime? (6,3)
I believe the answer is:
lights out
I believe this is a double definition.
'runs away' is the first definition.
('light out' can mean run away in US slang)
'at bedtime?' is the second definition.
(I've seen this before)
(Other definitions for lights out that I've seen before include "Goes off quickly" , "Bedtime signal" , "Time to switch off" , "Suddenly disappears" , "when it gets dark" .)