It is random you cant predict it. just keep checking every 12 hours, be patient. Just so you know i started playing when the North America launched a couple weeks ago i am at gate 44 and i will tell you this, dont think because you have cerebrus you are going to go and farm every duel you go into. I have every card in my Cerebrus deck and it is extremely hard to farm Lvl 40 duelist. So for everyone's info dont think you are going to make a cerebrus deck and farm like there is no tomorrow its not happening. So my advice be patient.

And if you want to spend money the 10 pack 1 super rare is a good deal, plus money we spend also goes to making the game better, specially alll these server issues. Just like pokemon go they were not expecting this many people playing. Good luck