If the pool had 1 MS/s and some miner appears with 9 MS/s he will get 90% reward which is fair. No matter if the pool had no blocks for even a couple of days before that.
Nobody could predict when the block is found (miners, pool owners, nobody). It is impossible to rent hashpower and be "on time" to find a block.
Don't worry, PPLNS system that is used in our pool prevents the pool hopping.
2Miners mining pools: https://2miners.com/
2CryptoCalc mining profit calculator: https://2cryptocalc.com/