Nimrod,

Most of the national and world events are 3 day events. These can be shot on the first day but you have to Move and be out on the hill early. It is much simpler to shoot these events in two days. Because if you don't get out early on Friday then Saturday and Sunday the places are usually packed with people and you may not get your targets in in time.

But if you are truely asking about the world qualifiers, If it is any thing like Michigan the World Qualifiers are normaly much smaller and you could shoot them most likely any day durring the weekend they are being held.
Hope this helps.

Regards,
OBS