Airsoft bomb hellp , need 2 more digit for second

Hello people, Can anyone help me, I make airsoft bomb I
found this code and perfectly suits me, but I need a second,
means more 2 digit 7 segment display but i dont now how to do it,
please help.
if need be I’ll pay

/* 	Arduino two digit 7 Segment Display Counterdown Timer
	Dev: Michalis Vasilakis // Date: 30/3/2016 // Ver.1
	Find more info at www.ardumotive.com					*/

//Library
#include "SevenSeg.h"

//Seven Seg
SevenSeg disp (10,9,8,7,6,11,12); //Defines the segments A-G: SevenSeg(A, B, C, D, E, F, G);
const int numOfDigits =2;	      //number of 7 segments
int digitPins [numOfDigits]={4,5};  //CC(or CA) pins of segment

//Constants
const int startBT = 2;
const int changeBT = 3;
const int setBT = 13;
const int dotPoint1=A0; //left digit
const int dotPoint2=A1; //right digit
//Variables
String number="00";
int digit1=0;
int digit2=0;
int start, change, set;
int setPoint=0;
int countdown;
//Useful flags
boolean countFlag=false;

void setup()
{
	pinMode(startBT, INPUT_PULLUP);
	pinMode(changeBT, INPUT_PULLUP);
	pinMode(setBT, INPUT_PULLUP);
	pinMode(dotPoint1, OUTPUT);
	pinMode(dotPoint2, OUTPUT);
	//Defines the number of digits to be "numOfDigits" and the digit pins to be the elements of the array "digitPins"
	disp.setDigitPins ( numOfDigits , digitPins );
	//Only for common cathode 7segments
	disp.setCommonCathode();
	//Control brightness (values 0-100);
	disp.setDutyCycle(60);
	disp.setTimer(2);
    disp.startTimer(); 
}

void loop()
{
	//Read buttons state
	start = digitalRead(startBT);
	change = digitalRead(changeBT);
	set = digitalRead(setBT);
	
	
	if (set == LOW && !countFlag){
		delay(500);
		if (setPoint<2){
			setPoint++;
		}
		else{
			setPoint=0;
		}
	}
	
	//Start counting...
	if (start == LOW && setPoint==0
	){
		delay(500);
		if (!countFlag){
			countFlag=true;
			countdown = number.toInt();
		}
		else{
			countFlag=false;
		}
	}
	if (change == LOW && setPoint == 1 && !countFlag){
		delay(500);
		if (digit1<9){
			digit1++;
		}
		else{
			digit1=0;	
		}
		number=String(digit2) + String(digit1);
	}
	if (change == LOW && setPoint == 2 && !countFlag){
		delay(500);
		if (digit2<9){
			digit2++;
		}
		else{
			digit2=0;	
		}
		number=String(digit2) + String(digit1);
	}
	//Control dot points
	if (setPoint==0){
		digitalWrite(dotPoint1,LOW);
		digitalWrite(dotPoint2,LOW);
	}
	else if (setPoint==1){
		digitalWrite(dotPoint1,HIGH);
		digitalWrite(dotPoint2,LOW);
	}
	else if (setPoint==2){
		digitalWrite(dotPoint1,LOW);
		digitalWrite(dotPoint2,HIGH);
	}
	//////////Counter Control///////////
	if (countFlag){
		if (countdown>0 && countdown<=10){
			countdown--;
			delay(1000);
			disp.write("0"+String(countdown));
		}
		else if (countdown>10){
			countdown--;
			delay(1000);
			disp.write(String(countdown));
		}
		else if (countdown==0){
			disp.write("00");
			delay(500);
			disp.write(" ");
			delay(500);
		}
	}
	else{
		disp.write(number);

	}
	
}

ISR( TIMER2_COMPA_vect ){
 disp.interruptAction ();
 }

http://www.instructables.com/id/Arduino-Countdown-Timer-With-Setup-Buttons/?ALLSTEPS

Do you want instructions on how to make a timer or a bomb? What is an airsoft bomb.?

http://www.instructables.com/id/Arduino-Ticking-Time-Bomb/