User blog comment:SayuriDarling/The Demigod Diaries Official Discussion Blog/@comment-4515675-20120815183719/@comment-399102-20120815185542

Yes! I agree. If it's one thing I dislike about Rick Riordan, he has no conscious when it comes to continuity errors! Your correct, the quest that they took did happen during Winter Solstice. But according to Leo, two months had passed since their quest which would have made it February.

It seems like Rick Riordan is basing the time line on when the book was actually published, which was October, which would mean Leo is correct that it is December, two months later. But we know the quest didn't occur in October.

It's the same in the Son of Neptune. Percy is said have slumbered for 8 months. But according to the Lost Hero, he had been missing for three days in mid December. But it's June, almost summer solstice in the Son of Neptune, which means he really slept for 6 months. But like I said, it seems like RR is basing it on publication because 8 months from October, when the Lost Hero was released, is June.