Oh....forgot to reply to the other part....The eighth day is considered a new creation....the new Adam....not sure about the resting in the grave part but I know Jesus appeared to his disciples on a Sunday following his ressurection as well.

My priest told me that Saturday is still the Sabbath and very holy, but as new creatures we enter into the new birth and celebrate on Sunday.

It's like your snake symbol with the head biting the tail....from Sunday to Sunday....the first day and new creation intersect cause you are born again....it's kindof mysterious....I guess it's something to meditate on and one could come up with all sorts of revelations.