Did anyone calculate the rate every 20 days? Is 20% the yearly compounded rate (year 1) assuming PoS is minted every 20 days? So that's about 0.5% or so every 20 days (for comparison, Hobonickels pays out 2% every 10 days).
It's not minted every 20 days. The PoS STARTS after 20 days.
"PoS blocks will be generated after you hold some coins in your wallet for certain period of time. For MintCoin the minimum requirement is 20 days."