Cavalier's horse jumping everything, over time (7)
I believe the answer is:
gallant
'cavalier's' is the definition.
(thesaurus)
'horse jumping everything over time' is the wordplay.
'horse' becomes 'nag' (term for an old horse).
'jumping' is an insertion indicator (some letters jump around or over others).
'everything' becomes 'all' (all things).
'over' says the letters should be written backwards.
'time' becomes 't' (abbreviation).
'nag' placed around 'all' is 'nallag'.
'nallag' backwards is 'gallan'.
'gallan'+'t'='GALLANT'
(Other definitions for gallant that I've seen before include "Daring" , "Brave; courteous" , "Chivalrous - dashing" , "Courageous - politely attentive to women" , "lover" .)