10 Points: Halo Question ?

Whenever we have a daily or weekly challenge where we have to complete a mission (the weekly challenge is "Not in the race", complete any campaign mission on heroic in 15 minutes with Black eye on), do we have to do the whole mission ? Like, when you're selecting a mission like "Winter Contingency", there's mission start, rally point alpha, and rally point bravo. Can just do one of those, or I have to play all three (the whole mission).