In the system you can select rankings for 1) the previous 12 months or 2) a specific ski year. For the ski year rankings, those are from nationals to nationals. The previous 12 months scores look back over the last 12 months and scores roll off the system weekly. For nationals qualification, the cut-off is 3 weeks before nationals and uses the previous 12 months scores on that date. So, for 2012 Nationals qualification, scores from approximately Mid-July 2011 thru Mid-July 2012 will count for the ranking list. If you don't qualify that way, there are last chance qualifiers by beating the cutoff score in a record tournament during the 3 week period between the cutoff date and the start of nationals.
Hope this helps.