Film legend is on time (7)
I believe the answer is:
footage
'film' is the definition.
(I know that footage is a type of film)
'legend is on time' is the wordplay.
'legend' becomes 'foot' (I can't justify this - if you can you should believe this answer much more).
'is on' says to put letters next to each other (in a down clue, letters appear on others).
'time' becomes 'age' (an age is a period of time).
'foot'+'age'='FOOTAGE'
Can you help me to learn more?
(Other definitions for footage that I've seen before include "Length of film" , "Part of film" , "Film that has been shot" , "quantity shot" , "Quantity of film (of event)" .)