not a moment to spare
At the last possible moment before it is too late; just in the nick of time. Quickly, you have to shut down the reactor—there isn't a moment to spare! A: "The surgeon has just arrived." B: "And not a moment to spare! This patient needs an operation immediately!"
not a moment to spare
and without a moment to sparejust in time; with no extra time. Hurry, hurry! There's not a moment to spare! I arrived without a moment to spare.