Just my feedback about this matter:
It's not fair, it doesn't give all the players the same chances... you should either set a timetable or don't give any history entries at all...
While there are players that would like to participate yet have not yet been able to, that is tied to the nature of this event.
this is exactly the kind of nature I wish I'd never find in a mmo event. I'd rather camp for hours a non instanced NM against other groups... at least that's not random.