When exactly does the API sends its reply when unlocking a door?

I use the /smartlock/{id}/action and {"action": 3} as the body to open a door (not sure anymore why not the explicit /smartlock/{id}/action/unlock one, it has been some time).

The call triggers the open action as expected and I wanted to ask whether someone knows when the 204 reply from the API comes back

  • as soon as it authenticated the call
  • when it starts the opening process
  • when the lock has finished opening
  • when the lock has been released (and the door is now locked by the movinig-thingie-I-do-not-know-the-name-in-English latchbolt)

I am away from my lock and cannot test visually (at least the parts that are visible) so if someone has a clue I would be grateful.