Corrected entry: On page 99, it mentions that Harry and his classmates have Astronomy at midnight on Wednesdays. But on page 173, it says, "Wednesday night found Hermione and Harry sitting alone in the common room, long after everyone else had gone to bed. The clock on the wall chimed midnight when the portrait hole burst open." They should have been in Astronomy at this time.
Issabee
14th May 2006
Correction: Since the date changes at midnight, it is possible that the "midnight on Wednesday" they are referring to actually occurs on what we would think of as Tuesday night. Therefore, the scene in the common room, which took place on Wednesday night proper, would have been the NEXT night.