Actual date of Lockhart's Valentine's Day celebration?

As the HP Lexicon website points out, Valentine's Day was actually on a Sunday in 1993. Professor Lockhart mentions that the dwarves will be delivering Valentine's to classes throughout the day, so apparently Hogwarts is having classes on this Sunday. Has any explanation ever been found? Perhaps classes were cancelled on the previous Friday or following Monday for some reason, and are being held on Sunday instead? -- UnicornWolf (talk) 14:20, February 24, 2014 (UTC)