Boy, he leaves here before ten (3)
I believe the answer is:
rex
'boy' is the definition.
'he leaves here before ten' is the wordplay.
'leaves' is a deletion indicator.
'before' is a charade indicator (letters next to each other).
'ten' becomes 'x' ('X' can be a synonym of 'ten').
'here' with 'he' taken out is 're'.
're'+'x'='REX'
(Other definitions for rex that I've seen before include "Part of official title of a king" , "See 6" , "King - Harrison?" , "Dog's name; king" , "King (Latin); cat breed" .)