After the mining block had been unlocked and system will send payment to miners. In my little knowledge system is also using PPLNs as more profit for loyal miners. Let's discuss more about it.

You need to have a look at http://give-me-coins.com/support/faq/what-is-pplns/

"PPLNS favors constant and/or occasional loyal pool members over pool hoppers. As you might have seen, each time we find a LTC block the pools hash-rate peaks instantly. This is due to pool hoppers starting to mine. They are betting for a “quick win” (like round two above) with low shares per round. If the round exceeds a certain amount of shares they “hop” to another proportional pool which started a new round more recently. This assures better rewards for pool hoppers over occasional or constant miners which are loyal to their pool. Pool hopping however implies that pool hoppers need to know when a round is started and how much shares are considered for reward. This is very easy with proportional reward system."