Just looked this up: "The 11th hour meaning is the last moment or almost too late"
So you could say: 'The Rebels brought the shield down at the 11th hour', but I'm not sure how you can apply this phrase to this interaction between Saw and Luthen. They're both already at war with the Empire; this moment signifies a new understanding of the sacrifices required, or of how they might work together in future, but I don't understand how it's the 'last moment' of anything.
Maybe I'm being pedantic, and it's just a reference to it being the 11th episode. Enjoyable watch, nevertheless.