Yes, but that is still one of several interpretations of that statement. For me it will fly 690 km total, all of it at an average speed of 460 km/h.

If you're telling me I somehow need to factor in deceleration and acceleration of the plane, or some other unknown speed for the rest of the distance between Warsaw and ??????...

well, I stand by my answer while mentally burning down mr-riddle's house out of frustration XS