http://www.wdwinfo.com/wdwinfo/dining/pscalc/dispscalc.html
180 + 10 is a perk for Disney resort guests. Using their resort confirmation number, they can start making reservations at their 180 day mark. But they do not have to call or go online day by day; they can make all their reservations for up to 10 days of their trip at their 180 day mark.