http://www.go-pokemon.com/op/news/articles/38.html
'momWorlds Invitation Deadline Extended
Important information regarding attendance confirmation deadline.
Due to the short time between Canadian Nationals and the invited-player confirmation deadline of July 14th, Pokémon Organized Play has extended the deadline for all players worldwide to July 21st, 2008. Players who do not confirm their attendance to the World Championships by that date are subject to losing their invitation to the event.
POP will announce the final number of Last Chance Qualifier invitations shortly after the July 21st deadline.