This is not a bank or investment firm paying steady interest on your money, this is mining, everybody should clearly understand this. You need to have your wallet open all the time or as much as you can, otherwise you may get nothing.
It should work like this:
"POS mining" process is just about holding coins and leaving your computer on. Only matured coins (coins stored in a wallet over 24 hours) are eligible for POS. Each block (every 45 seconds), a random lucky coin is selected to be the next "miner". If a node with the selected coin wallet is running, it will collect the transactions, make a block, and send it to the rest of the network and collect the fees. If the computer is turned off, however, then the entire network will have to select a different coin to make the transaction. This time, the unresponsive wallet will be ignored.