"I, Drakness Tenebrosus, hear the command of the one that has been blessed with the Mark of Tiamat. With my conviction and loyalty to her, I shall make sure that the command of Champion Equinox shall be done by his will." Drakness Tenebrosus stated.
Adrian could no longer answer all the questions that the Dark Dragon King asked him. This is a command and not a suggestion which is why he already issued the command when he already gave the important bits of information. From the Dark Dragon King's expression, it seems that one of the dragons have close ties to the angels.
Adrian already has a battle plan in mind, but he also needs a few days of preparation. He told Drakness Tenebrosus to come back in Avalon with his dark dragon army a day before the attack date. He will need to brief them in order to make the plan a success.