The payout days are always average - i.e.: Let's say Dash Nodes pay out every 10 days (as a pure example - this has nothing to do with luck, but only how the coin determines that payout frequency) - if e.g. 2 Dash Rewards are being paid by out by 2 different nodes on the same day, the average payout is every 5 days. It always depends on how many nodes are running and this is the average, the more nodes the more frequent payouts, because our nodes are always paid proportionally to all users who have shares of the respective coin. That's why it also fluctuates, depending on how many nodes are currently active.