[Romulus]

we are now living in the Eighth "Day"

You probably know this is the reason that free-standing baptistries in the first millennium were typically octagonal in design.

[neocon]

That's very likely, especially as Baptism is a symbolic drowning - a death to the life of world - followed by a rising to new life in Christ.

As I understand it, certain churches (Romanesque?) built to house important relics were also commonly octagonal in design.

The chapel at Mt. Savior Monastery in Elmira, NY is designed as cruciform (equal-arm) with an octagonal transept, deliberately, to bring to mind the Eighth "Day".

Finally, of course, the concept demonstrates that the early Church did not subscribe to a literal interpretation of Genesis, but that's a topic for another day.