trains – How late can I enter a Nightjet Liegewagen or Schlafwagen?

I've noticed that when I try to book a Nightjet ticket from Frankfurt Süd to Berlin (departure 00:54), I can reserve a seat but not a place in Liegewagen or Schlafwagen. When I try to book the same train but starting in Basel (exit 21:13), those alternatives appear. I suppose that the night outings or the early morning arrivals are blocked in Liegewagen Y Schlafwagen. At what times can I not enter or leave these compartments?