Pushing that button, seemed to kill them all, and they knew that pushing the button killed everyone which is why the assistant didn't want to do it. After the drones fainted/died... Then Boom!
Kiera is inconsistent about how she believes time travel works.
And the monologue at the beginning is still a lie and grossly inaccurate.
But it's "nice" to see what happens when you can't pay your life debt.