By midday, young lady is back in her bunk (4)
I believe the answer is:
abed
'her bunk' is the definition.
I can't tell whether this definition defines the answer.
'by midday young lady is back' is the wordplay.
'by midday young' becomes 'ab' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'lady' becomes 'De'.
'is back' says the letters should be written backwards.
'de' in reverse letter order is 'ed'.
'ab'+'ed'='ABED'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for abed that I've seen before include "given blanket coverage?" , "laid up" , "going to sleep?" , "Having not got up" , "how we all hope to go?" .)