How far is it fron layer 5th to layer 6th

The "Garden of Eternal Fortunes" (盆景箱) of bondreud- its elevation and travel time make no sense. Riko's team endured a long Interference Unit journey, but Mitty/Nanachi took an elevator straight to the bottom in seconds. The sky in the 6th Layer also shows no sign of the Garden's rock ceiling above.

What's the deal? Spoilers welcome, I need a lore master!