I don't know. Some were instant (Sahagin from Sastasha), others took some time (Titan).

Honestly, I spam content just because I like to. Most times, I wouldn't even know I got a card until after a dungeon and I go to vendor all the spoils I collected. I had did Amdapor Kill hours before I spammed Primals. Go to sell items to vendor, and I had a Demon Card.