When you are in Time Machine, you can press the red close button at the top left of the window being viewed to close Time Machine. When you do so, the window itself will not close, just Time Machine. This is also useful if you have a slower computer and you want to cancel Time Machine while it is animating to the Space visual. You can press the close button on the window in question at any time during the animation, and it will revert back to it's pre-Time Machine position. You don't have to worry about the window closing.

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