Yugioh - Wulf, Lightsworn beast. Can you special summon it whenever you want?

This was the situation, I had Koaki Meiru Dragon on the field, he uses card trooper to dump wulf into the graveyard. so at the time he couldnt special summon. in his next turn he dumps another one but still cant special summon it. later on when koaki meiru is destroyed, he says he can choose to special summon them. i try explaining that I dont think you can just special summon them anytime in the duel afterwards. can someone answer this for me?