Comment modifier le temps dans un programme Arduino?

Bonjour,
dans mon programme, ma plage de temps qui est modifier par mon potentiomètre va de 0 seconde à 30 secondes,
mon objectif est que la plage de temps soit de 0 seconde à 15 minutes.
Comment faire?

Ceci est pour un arrosage automatique permettant de piloter 12 électrovannes.

int led1=12;
int led2=13;
int led3=2;
int led4=3;
int led5=4;
int led6=5;
int led7=6;
int led8=7;
int led9=8;
int led10=9;
int led11=10;
int led12=11;

int v,v2;

int pot=0;


const int buttonPin2 = A2;
const int buttonPin3 = A3;
const int buttonPin4 = A4;
const int buttonPin5 = A5;
const int buttonPin6 = A14;
const int buttonPin7 = A15;
const int buttonPin8 = A8;
const int buttonPin9 = A9;
const int buttonPin10 = A10;
const int buttonPin11 = A11;
const int buttonPin12 = A12;
const int buttonPin13 = A13;


const int buttonPin = A1;

int buttonState = 0;

int buttonState2 = 0;
int buttonState3 = 0;
int buttonState4 = 0;
int buttonState5 = 0;
int buttonState6 = 0;
int buttonState7 = 0;
int buttonState8 = 0;
int buttonState9 = 0;
int buttonState10 = 0;
int buttonState11 = 0;
int buttonState12 = 0;
int buttonState13 = 0;

int etat=0;
int prevetat=0;


void setup() {


pinMode(buttonPin2, INPUT);
pinMode(buttonPin3, INPUT);
pinMode(buttonPin4, INPUT);
pinMode(buttonPin5, INPUT);
pinMode(buttonPin6, INPUT);
pinMode(buttonPin7, INPUT);
pinMode(buttonPin8, INPUT);
pinMode(buttonPin9, INPUT);
pinMode(buttonPin10, INPUT);
pinMode(buttonPin11, INPUT);
pinMode(buttonPin12, INPUT);
pinMode(buttonPin13, INPUT);

pinMode (led1,OUTPUT);
pinMode (led2,OUTPUT);
pinMode (led3,OUTPUT);
pinMode (led4,OUTPUT);
pinMode (led5,OUTPUT);
pinMode (led6,OUTPUT);
pinMode (led7,OUTPUT);
pinMode (led8,OUTPUT);
pinMode (led9,OUTPUT);
pinMode (led10,OUTPUT);
pinMode (led11,OUTPUT);
pinMode (led12,OUTPUT);

Serial.begin(9600);

pinMode(buttonPin, INPUT);

}

void loop() {


buttonState = digitalRead(buttonPin);

buttonState2 = digitalRead(buttonPin2);
buttonState3 = digitalRead(buttonPin3);
buttonState4 = digitalRead(buttonPin4);
buttonState5 = digitalRead(buttonPin5);
buttonState6 = digitalRead(buttonPin6);
buttonState7 = digitalRead(buttonPin7);
buttonState8 = digitalRead(buttonPin8);
buttonState9 = digitalRead(buttonPin9);
buttonState10 = digitalRead(buttonPin10);
buttonState11 = digitalRead(buttonPin11);
buttonState12 = digitalRead(buttonPin12);
buttonState13 = digitalRead(buttonPin13);



if (buttonState == LOW) {
digitalWrite(led1,HIGH);
digitalWrite(led2,HIGH);
digitalWrite(led3,HIGH);
digitalWrite(led4,HIGH);
digitalWrite(led5,HIGH);
digitalWrite(led6,HIGH);
digitalWrite(led7,HIGH);
digitalWrite(led8,HIGH);
digitalWrite(led9,HIGH);
digitalWrite(led10,HIGH);
digitalWrite(led11,HIGH);
digitalWrite(led12,HIGH);

v=analogRead(pot);
v2=map(v,0,123,0,5000);

int x=v2;


digitalWrite(led1,LOW);
if (buttonState2 == HIGH) {
delay(x);
} else{
delay(0);
}
digitalWrite(led1,HIGH);



digitalWrite(led2,LOW);
if (buttonState3 == HIGH) {
delay(x);
} else{
delay(0);
}
digitalWrite(led2,HIGH);



digitalWrite(led3,LOW);
if (buttonState4 == HIGH) {
delay(x);
} else{
delay(0);
}
digitalWrite(led3,HIGH);



digitalWrite(led4,LOW);
if (buttonState5 == HIGH) {
delay(x);
} else{
delay(0);
}
digitalWrite(led4,HIGH);



digitalWrite(led5,LOW);
if (buttonState6 == HIGH) {
delay(x);
} else{
delay(0);
}
digitalWrite(led5,HIGH);



digitalWrite(led6,LOW);
if (buttonState7 == HIGH) {
delay(x);
} else{
delay(0);
}
digitalWrite(led6,HIGH);



digitalWrite(led7,LOW);
if (buttonState8 == HIGH) {
delay(x);
} else{
delay(0);
}
digitalWrite(led7,HIGH);


digitalWrite(led8,LOW);
if (buttonState9 == HIGH) {
delay(x);
} else{
delay(0);
}
digitalWrite(led8,HIGH);



digitalWrite(led9,LOW);
if (buttonState10 == HIGH) {
delay(x);
} else{
delay(0);
}
digitalWrite(led9,HIGH);


digitalWrite(led10,LOW);
if (buttonState11 == HIGH) {
delay(x);
} else{
delay(0);
}
digitalWrite(led10,HIGH);



digitalWrite(led11,LOW);
if (buttonState12 == HIGH) {
delay(x);
} else{
delay(0);
}
digitalWrite(led11,HIGH);



digitalWrite(led12,LOW);
if (buttonState13 == HIGH) {
delay(x);
} else{
delay(0);
}
digitalWrite(led12,HIGH);




buttonState = digitalRead(buttonPin);
}else{
digitalWrite(led1, HIGH);
digitalWrite(led2, HIGH);
digitalWrite(led3, HIGH);
digitalWrite(led4, HIGH);
digitalWrite(led5, HIGH);
digitalWrite(led6, HIGH);
digitalWrite(led7, HIGH);
digitalWrite(led8, HIGH);
digitalWrite(led9, HIGH);
digitalWrite(led10, HIGH);
digitalWrite(led11, HIGH);
digitalWrite(led12, HIGH);

}
}