How many weeks are there in a One Piece year? During the time-skip Luffy was sent to Rusukaina to train with Rayleigh. When they arrive Rayleigh introduces the island as follows.


  Rusukaina is home to the "48 seasons", a brutal island where the climate changes once a week.


This quote makes me wonder about the number of weeks in a year in One Piece. One would expect there to be 52 weeks as there are in our human world. So what about in the One Piece world? Are there 48 weeks in a year, 52 weeks in a year, or maybe a different number?
I'm going to go out on a limb, and suggest that "once a week" is not precise. Most people would find it more convenient than "once every 7.6 days" or worse "every 1.1 weeks".

While it would be interesting to have complicated shenanigans, and I have no definitive proof that there aren't any, I think it's more just quick communication.