Sometimes there might be a short delay in fitting customer equipment to a new airliner, although any plane should be essentially ready to go from the factory. A month on the ground at probably a million dollars in lease or money costs should never be part of the calculus for anything but the first hull.
Route proving*, staff familiarization, CASA last minute stuff all takes time, but all of that should have been satisfied with the first plane. An aircraft untouched on an apron obviously is contributing nothing to those activities either.
I did hear that the second and third aircraft were going to be stored for awhile owing to lack of sufficient crew, but I find that hard to credit. (Except of course when I consider the context)
*route proving: why? What is learned ferrying aircraft all over routes already well lubricated by previous similar types?