Looking at potential storylines for season 3, it is clear that the secret to time travel may be unveiled. Before Isla died she brought Micah’s journal back in time with her where it was bagged up as evidence and stored away. This means that the secret to time travel is yet to be discovered, this may be a lead for season 3.
Some more leads for season 3 include the potential bleeding of timelines, Zoe and Emily keep getting flashbacks of a future that isn’t going to happen suggesting that they are being sent from another timeline. Then, over the credits was the sound of an alien pulse which further hints that Bill hasn’t actually averted the alien invasion future.