snip off a length

I don't look on poetry as closed works. I feel they're going on all the time in my head and I occasionally snip off a length.

—John Ashbery, London Times (23 Aug 1984)

long enough

Paradise Lost is one of the books which the reader admires and puts down, and forgets to take up again. None ever wished it longer than it is. Its perusal is a duty rather than pleasure.

—Samuel Johnson, “Milton,” The Lives of the English Poets

can't take out anything

Disce quod ignoras: Marsi doctique Pedonis
saepe duplex unum pagina tractat opus.
Non sunt longa quibus nihil est quod demere possis,
sed tu, Cosconi, disticha longa facis.

Learn what you don't know: one work of (Domitius) Marsus or
    learned Pedo
often stretches out over a doublesided page.
A work isn't long if you can't take anything out of it,
but you, Cosconius, write even a couplet too long.

—Martial

narcissism

We can put up with someone’s narcissism providing it makes interesting reading and it doesn’t run on too long.

–Charles Simic, ‘The Power of Ruins’ (review of Louise Glück’s Averno in NYRB)

at length

The length of a film should be directly related to the endurance of the human bladder.

—Alfred Hitchcock