It depends on the type of feature film. If it is an animation film, the editing starts at the very beginning. The editors have to be involved with all of the pre-production so that they are prepared to animate the movie. If the film is, say an action movie, the editor can be on the set of the movie checking in with the cinematographers and the directors to make sure everything is going alright. Generally speaking, the editing process doesn't start until the post-production stage. This is after all the filming has been completed. The director sits down with the editor to talk about his vision and what he wants the film to look like. Then the editor edits the film.
Hope this helps!
