Sorry for my poor English!

You need an Arduino（NANO,MINI,UNO、、、）
And a 28BYJ48 stepper

If your fish food's diameter more than 2mm, you will need a little Screw(prt0003)

Arduino Code

//#include "Stepper.h"
//#define STEPS 100

Stepper stepper(STEPS, 2, 3, 4, 5);//CHANGE TO YOUR PIN

int previous = 0;
long interval = 7200000L;//Interval ,HOW LONG, 7200000L MEAN 2 HOURS
unsigned long previousMillis = 0;

void setup()
{
stepper.setSpeed(80);
}

void loop()
{
unsigned long currentMillis = millis();
if(currentMillis - previousMillis > interval) {
previousMillis = currentMillis;
stepper.step(3500); //HOW MUCH
}
if(currentMillis < previousMillis){ //OVERFLOW CHECK
previousMillis=currentMillis;
}

}

Doesn't Matter

Doesn't Matter