However, it was later stated that 22 November was a Tuesday, which it was in 1994.
Although the series, according to the timeline derived from the Chamber of Secrets reference, is set in the nineties, the book often seems as though it is set more in the present time.
Often when dates are given, they are given with a day of the week that does not match with that date as it in actual history.
One such example occurs in Harry Potter and the Prisoner of Azkaban when Sybill Trelawney refers to 16 October as Friday, although 16 October 1993 was a Saturday.
Another problem exists regarding Rubeus Hagrid's tenure as Hogwarts's gamekeeper.
It is implied throughout the series that Hagrid was given that position within a few years of his expulsion from school in 1942.
Also, in Harry Potter and the Goblet of Fire it is said that the Champions were chosen on Saturday 31 October, but 31 October was a Monday in 1994.
In addition, considering the Harry Potter universe is a fantasy world, it's possible that certain dates may differ between it and the "real world".