It seems that for the BA shipments at least, which is my only reference point, it was a week. Whether that it because they were just desperate to get them out before end of year or not I don’t know.
What I thought was a little odd, and never mentioned here, was that when I was called to ask if I could take delivery this week (I was called just before Christmas) the lady told me “your car should be arriving next week” I told her I knew it had arrived the night before! She said it could have done but she wasn’t sure.
So the guys that work there clearly don’t know anywhere near as much as people here. So I would take anything they say with a pinch of salt. Not knocking them, they just aren’t as motivated as people here to know this stuff tbh.