Unexpected debt I'm beginning to experience when retirement's due (7)
I believe the answer is:
bedtime
'when retirement's due' is the definition.
(retiring can mean going to bed)
'unexpected debt i'm beginning to experience' is the wordplay.
'unexpected' indicates anagramming the letters.
'beginning to' suggests taking the first letters.
The initial letter of 'experience' is 'e'.
'debt' with letters rearranged gives 'bedt'.
'bedt'+'im'+'e'='BEDTIME'
(Other definitions for bedtime that I've seen before include "Hour to retire" , "when story comes out?" , "when one's due for retirement?" , "eleven o'clock?" , "When someone retires" .)