Setting time frame in Arduino Uno
Could you tell us which multiplexer IC you are using? This way, we can help you better. Also, why do you need the 8 second cycle? Does it matter if it's a little shorter or longer? If timing does not have to be very precise it would make things a lot easier.

By the way: you say there are 30 sensors, but your table has 32...

The following pseudocode will not work on your Arduino, but you can use the same structure.

int sensorArray[32] // we will store our 32 sensor values here

// these pins control the multiplexer chips
int selectPinZero = 8;
int selectPinOne = 9;
int selectPinTwo = 10;

// these pins will receive the sensor values from the multiplexer chips
int inputPinOne = 0;
int inputPinTwo = 1;
int inputPinThree = 2;
int inputPintFour = 3;

void setup(){
    // make sure the correct pins are inputs and outputs
    pinMode(selectPinZero, OUTPUT);
    pinMode(selectPinOne, OUTPUT);
    pinMode(selectPinTwo, OUTPUT);

    pinMode(inputPinOne, INPUT);
    pinMode(inputPinTwo, INPUT);
    pinMode(inputPinThree, INPUT);
    pinMode(inputPinFour, INPUT);
}

// all done, now keep reading the sensors
void loop(){

    // set selectPins so that each Multiplexer will output its first channel
    digitalWrite(selectPinZero, HIGH); // or low, depending on your Multiplexer IC
    digitalWrite(selectPinOne, HIGH); // or low, depending on your Multiplexer IC
    digitalWrite(selectPinTwo, HIGH); // or low, depending on your Multiplexer IC

    // start reading sensors

    int i = 0;
    while(i&lt;32){
        sensorArray[i] = analogRead(inputPinOne);
        i++; // variable i was 0, now 1 

        sensorArray[i] = analogRead(inputPinTwo);
        i++; // variable i was 1, now 2 

        sensorArray[i] = analogRead(inputPinThree);
        i++; // variable i was 2, now 3

        sensorArray[i] = analogRead(inputPinFour);
        i++; // variable i was 3, now 4

        /*
        use digitalWrite() on all the selectPins to make the Multiplexer IC output the next channel
        */

        delay(1000); // wait 1000 milliseconds
    }

    /*
    this will repeat until all 32 sensors are read and stored in the array
    */

}


This code is by no means optimized, but written to make it easy for you to understand. Good luck!