NBX staking follows the Cardano protocol, which is a 4 epoch process starting the epoch after you register for staking. In the first epoch after staking, a snapshot is taken of the stake amount. In the second epoch, your staked ADA helps to secure the blockchain. In the third epoch, rewards are calculated. Finally, in the fourth epoch, rewards are distributed. This process means that rewards can take up to 20 days the first time you stake. After that, you will be paid rewards every 5 days.