Stake weight is basically the amount of coins you have in your wallet times the age of the incoming transactions, in days.. So your stake weight is expected to go up until your wallet solves a valid block. When exactly you will find a block is unpredictable and based on three factors:

1) stake weight
2) net weight, the estimated coin age of all coins being staked on the network
3) luck

So as your stake weight gets bigger in proportion to net weight, your wallet is more likely to find a PoS block.