Dunkin Donuts $.99 Coffee/Tea Any Size

So... I have another coffee deal with incomplete information.  Dunkin' Donuts is offering $.99 iced or hot coffee and tea from 2 to 6pm (any size!).  This deal I have actually tried, so I know it is legitimate.

What I do not know is how long it will last.  Also, included in the $.99 deal is the flavored iced coffees that are inspired by the Baskin Robbins ice cream flavors.  Yum!