An Acceptable Time is a 1989 young adult science fiction novel by Madeleine L'Engle, the last of her books to feature Polyhymnia O'Keefe, better known as Poly (The Arm of the Starfish, Dragons in the Waters) or Polly (A House Like a Lotus, An Acceptable Time). Marketed as part of the author's Time Quintet (the other four volumes of which are called the Time Quartet), An Acceptable Time connects Polly's adventures with those of her parents, Meg Murry and Calvin O'Keefe, which take place a generation earlier. The book's title is taken from Psalm 69:13, "But as for me, my prayer is to You, O Lord, at an acceptable time."