... demanding information during leave (7)
I believe the answer is:
exigent
'demanding' is the definition.
('exigent' can be similar in meaning to 'demanding')
'information during leave' is the wordplay.
'information' becomes 'gen' (gen is a kind of information).
'during' means one lot of letters goes inside another.
'leave' becomes 'exit' ('exit' can be a synonym of 'leave'**).
'gen' going within 'exit' is 'EXIGENT'.
(Other definitions for exigent that I've seen before include "Urgent and taxing" , "Demanding immediate attention" , "Pressing and urgent" , "Urgent and exacting" , "Exacting, requiring much" .)