If you read the cold crashing thread, that question is answered right at #1.
1) When your beer is ready to bottle (determined by waiting 3 weeks and or testing with a hydrometer and getting matching readings 48 hours apart), pick up the LBK.
It's odd they included them as the recipe doesn't list them under the ingredients. It's up to you whether to use them or not. Each will add about 0.65% ABV. Personally, I wouldn't as the recipe as is is already 8.4% ABV.