There are a number of variables, but even when you are not actually getting a stake or minting payout, you are gaining coin age.  Coin age times your Pandacoin input amount or staking balance is your stake mining or minting power and the bases for rewards. So basically if you are running your Pandacoin wallet constantly, your  chances of more frequent rewards and sooner rewards are the best.  The others staking their Pandacoin also make a difference as well as some luck or randomness is involved. If you are not getting rewards your Pandacoin staking and minting power increases with age.

You can check the Minting tab for estimations of when you are likely to get rewards, it allows you to display your minting probability for a selected time frame.  It does take 30 days for new Pandacoin transactions to fully mature for staking. You can expect 2 1/2% annually as a target and it is paid out as you find blocks with your staking and minting powers vs the network difficulty and block targeting parameters. Your rewards once mature are also eligible to engage in staking so all in all your minting rewards are much like getting compound interest payments.