In this case means only in that moment, "just" in this sentence fits better and I find it easier too. Did I answered your question?

Example: You will hear this is colloquial speech. It requires a comma, and notice the changed wording in the last clause. He phoned me just then, when I was about to leave the flat.

because there is a pause after these words .

Then he turned to do it all in reverse. Then he picked up another box. Then came Alexia and then the stabbing.