Was in the top bunk and woke up too late? (9)
I believe the answer is:
overslept
'was in the top bunk and woke' is the definition.
I can't tell whether this defines the answer.
'up too late?' is the wordplay.
'up' becomes 'over'.
'too late?' becomes 'slept' (I am not sure about this - if you are sure you should believe this answer much more).
'over'+'slept'='OVERSLEPT'
Can you help me to learn more?
(Other definitions for overslept that I've seen before include "Was late rising" , "Failed to rise on time" .)