I have an interesting issue that's similar. I installed Seasons while I had a long-running file. When I opened that file, I found that due to the game being on Tuesday, the holidays did fall on Saturdays. It's been like that for a long time. But now it's gone all funny. The game is telling me that the holidays are Fridays now, and the kids get a day off school and the adults get a day off work (sometimes) but then on Saturday I get the notification of the holiday and everyone gets the moodlets and the special holiday wishes! Any idea what that's about?