This post claims to have an educated guess:

In a world in which Justice Jackson either knew or suspected that at least five of the justices would grant temporary relief to the Trump administration if she didn’t, the way she structured the stay means that she was able to try to control timing of the Supreme Court’s (forthcoming) review—and to create pressure for it to happen faster than it otherwise might have. In other words, it’s a compromise—one with which not everyone will agree