In the preview pages that were released last month, Drummer says that the problem with the Dowling-designed time machine is that the moment you switch it on, you limit future time travelers to being able to travel back to that point in time. Since the time machine didn't function prior to its moment of initial operation, it cannot propel people past that point.
Thus, the appearance of the future Planetary team members at that point of origin means two things: one, they will come back to witness the moment, and two, Elijah Snow never allows anyone else to have the time machine schematics.