The meet and greet was originally supposed to end on January 4, but it has officially been extended to last until January 31. (Rumors indicate that this meet and greet opportunity may eventually be extended past that date, but there is obviously nothing official announced yet.)
This has been one of the most popular meet and greet opportunities in all of the parks, with lines that are extremely long all day. If you want to meet Anna and Elsa, try to do so first thing. Meeting times are scheduled for 11:00 a.m., 12:00 p.m., 1:00 p.m., 2:00 p.m., 3:00 p.m., 4:50 p.m., 5:50 p.m., and 6:50 p.m. Be sure to check a Times Guide or the My Disney Experience app in case things change.