I'm not positive, usually they are made once you make a transaction, but it's been a long time since I have received interest since the rate has been zero for so long. Also, I'm not intimately familiar with Muslim culture, but I think the INTENTION of the rule against interest would not include these types of payments. They are really just called interest, because it's easier to understand it in terms of rate of return when the interest rate is nonzero, but no one is actually paying you interest. It is more like mining cryptocurrency with proof of stake in a sense. All of the SBD "interest" that you earn is newly created from that days reward pool and a portion of it is given to reward those who hold steem dollars. Trust me, my friend, there is no usury about this process and you are not taking money from any other person, it is part of the reward mechanism, and it was called interest because it's easier to understand it that way.