1. It's very individual but give them at least one week before they start eating .
2. If your water is aged you can and should start the next day . I woul perform at least 50% WCs daily especially in the starting 3-4 weeks .
3.You up and dose feedings according to their needs .
Pour food , give them 30 min to eat and vacum the leftovers(turn off filters during feedings if they are strong and use prefilter to prevent food and poop rotting in your filter ) . Do this 2-3 times a day and they will start eating eventually.
P.s ask the breeder what did he fed them with and try to start with their favorite food.