It would be unfair to know the next Pottermore clue before it was released. You can find a list of all the clues and answers on the link to the Pottemore Insider in related links.
The clue on day 2 was released at 9am GMT.
The Clue for Day Five was: What is the house number of the Headquarters for the Order of the Phoenix in Grimmauld Place?
August 4, 2011
August 5, 2011
August 2nd 2011.
The first clue was released at 8am GMT on July 31st 2011.
The aim is that you must find your way to pottermore. On that site you will find the magic quill, clicking that will let you register.
The only book left to be released on Pottermore is Harry Potter and the Deathly Hallows. A release date is currently unknown.
Each day a new clue was released which, if answered correctly, led to one of Pottermore's partner websites. The quill would be hidden somewhere on the main page of that website.
The Next clue is...../////////////////\\\\\\\\\\\\\\\\\\\\\\\\| under the rainbow... <3
They were released at different times everyday to allow for different schedules and timezones.
The house cup isn't announced on a regular schedule. There will be an update on the Pottermore Insider shortly before they tally up the next one.