We don't know yet. We're hoping that studying stabilized Fissures will give an idea of how to control passage through them, but right now it seems to be at random.

[He moves his hand from his face and brushes back a bit of hair that's slipped loose of the fins on his head.]

There's no evidence either way yet, but...the people studying the Fissures have theorized that because they also warp time, we might be able to go back to when we left from.