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There is an old saying "well begun is half done"-'tis a bad one. I would use instead-Not begun at all 'til half done.

John Keats (2015). “John Keats - The Man Behind The Lyrics: Life, letters, and literary remains: Complete Letters and Two Extensive Biographies of one of the most beloved English Romantic poets”, p.414, e-artnow
There is an old saying well begun is half done-'tis a bad one. I would use instead-Not begun at all 'til half done.