When I add command below in "RunOnce" in nLite, Office installs ok at the end of Windows installation (when Windows starts first time, bat command is executed and Office installs).
But I would like to be able to install it like the other nLite addons, when Windows installation countdown is still active (before installed Windows starts for the first time). Is that possible somehow?

I also need reply about this. Thanks in advance

Can anyone please answer my question?

I don't know if its possible with office but if you want it to install before the first boot you need to create a sfx archive and run it at T13.

there is plenty of information on how to do this here