Instaed of focusing on the number of rings my guess is that the bell ringing has to do with Killer said: it's the end of a year and the beginning of another.
Followed by the ship sailing in exactly one circle around marineford the message could very well be to meet in exactly 1 years time...
The issue Oda faced was really the way the SH crews experience thus far compares to all the other characters and crews and how that impacts story telling. Shanks has been travelling for over ten years since he met Luffy in chapter 1. He and his crew were already apparently very formidable and...
