You are wrong. During a year there will be a 23 hour day and a 25 hour day. For the hour before the 23 hour day, adding 24 hours to get tomorrow's date won't work, it will get the day after tomorrow's date. For the first hour of the 25 hour day, adding 24 hours will get the same day's date. For the hour after the 23 hour day, subtracting 24 hours will get the date two days ago. For the last hour of the 25 hour day, subtracting 24 hours will get the same day's date.