I'm a long time making a picture (5)
I believe the answer is:
image
'a picture' is the definition.
('image' can be a synonym of 'picture')
'i'm a long time' is the wordplay.
'a long time' becomes 'age' ('age' can be a synonym of 'long time').
'im'+'age'='IMAGE'
'making' acts as a link.
(Other definitions for image that I've seen before include "Vision" , "Likeness; metaphor" , "Purplish pigment; pool" , "Simulacrum" , "Picture; simile" .)