Just book early for a change (6)
I believe the answer is:
barely
'just' is the definition.
(synonyms)
'book early for a change' is the wordplay.
'book' becomes 'b' (abbreviation for book).
'for a change' is an anagram indicator.
'early' anagrammed gives 'arely'.
'b'+'arely'='BARELY'
(Other definitions for barely that I've seen before include "how streakers like to act?" , "Not quite" , "Just about or scantily" , "how naturists exist" , "how babies are born?" .)