Sallah: Give 'em hell, Indiana Jones.
Sallah: I miss the desert. I miss the sea. I miss waking up every morning wondering what wonderful adventure the new day will bring to us.
Indiana Jones: Those days have... come and gone.
Sallah: Perhaps. Then perhaps not.
Indiana Jones: I've believed in magic a few times in my life. I've seen things... things I can't explain. I've come to believe it's not so much what you believe... it's how hard you believe it.
Answer: There is a bit of dialogue en route to the airport when Voller sets the instrument that says, "the first hand sets the destination," as in the time you want to travel back to. This would make the device completely absurd in principle if true (that's why I wanted to mark it as a plot hole/stupidity). Since it's supposed not to open portals but just detect them, it can't be that there are infinite portals for every moment in time you can choose to go back to (and they even close). The sky, while vast, is not infinite. We then find out that it is a trick since it is set to actually bring you to just one destination, but they don't know it yet.
Sammo ★