Equal time needed by soldier, perhaps, on a horse (10)
I believe the answer is:
tantamount
'equal' is the definition.
(similar in meaning)
'time needed by soldier perhaps on a horse' is the wordplay.
'time' becomes 't' (abbreviation).
'needed by' means one lot of letters go next to another.
'soldier perhaps' becomes 'ant' (soldier is a type of ant).
'on' means one lot of letters go next to another.
'horse' becomes 'mount' (mount is a kind of horse).
't'+'ant'+'a'+'mount'='TANTAMOUNT'
(Other definitions for tantamount that I've seen before include "Equivalent in seriousness (to)" , "Equivalent in value (to)" , "Virtually equivalent (to)" , "Equal in value" .)