According to the main site the bonus should continue for 90 days after the end of the Preferred World status for new characters.

"These incentives will remain in place until the active player populations of the Worlds in question have grown to a specified number. Please note that once a World has been removed from the "Preferred World" category, the various bonuses will no longer be applied. In the case of newly created characters, these bonuses will continue for 90 days (including the day of creation) regardless of any change in World status."

Instead, the bonuses only last for 90 days after the creation of the character, which is very much not what it says.

Also, before anyone argues that is what it says, I suggest reading the last sentence a few times. If it was only after character creation it would read: "In the case of newly created characters, these bonuses will continue for 90 days after character creation regardless of changes in World status."