I got it as well... But you need to sell in the 5 day period items over $100...

Actually, you just need to create the listing during the promo period (listings created before the promo period but sold during don't qualify) - it would be silly to be able to list a 7-day auction on the 1st day of the promotion and then not have it qualify for the discount. The same applies for Good-til-cancelled listings, the discount will apply for the first 30-day cycle, then revert back to the standard fees after it ticks over.