One hour. There are two specials airing. The first is about Legends of Tomorrow and that's a full hour or 45/48 minutes once you cut the commercials out I believe. The second hour the same night is the "Dawn of the Justice League" special with interviews from Zack Snyder and Patty Jenkins. So that likely means footage from the Wonder Woman film as well as BvS footage. Also interviews with Henry Cavil, Gal Gadot, and Ben Affleck as well.
They didn't say who was the host or narrator for these though.
This is airing on Tuesday, Jan. 19 2016 at 8pm EST. I think that should be added to the opening post or the title if possible.
It's 2 30-minute specials
Legends airs at 9:00pm and Justice League at 9:30
Justice League is hosted by Kevin Smith and Geoff Johns
http://www.ew.com/article/2015/12/30/suicide-squad-trailer-cw-justice-league-special