No, not usually. Usually, it’s just a matter of where the gaps are in the yachts booking calendar. The only exceptions are:
1) Christmas and New Years’ weeks. Boats always book both these weeks, so they have a specific change over date from the Christmas charter to the New Years’ charter. Yachts may also want ten nights minimum over this period. They don’t do under a 7-night trip.
2) Bareboats (where you Captain yourself) in different parts of the world often have a Saturday to Saturday.