A typical error about single chip timer interrupt

 Analyze the following program. Why is the following program interrupted? Reality 40 (I wanted to program it as a 40S countdown) Hint: The problem lies in the delay subroutine

#include
#define uchar unsigned char
#define uint unsigned int
sbit p14=P1^4;
sbit p13=P1^3;
uint i,t,z=50;    
void delay()
{
while(z-- ); }

unsigned char code tab[] = 
{
                0XC0,//;0
                0XF9,//;1
                0XA4,//;2
                0XB0,//;3
                0X99,//;4
                0X92,//;5
                0X82,//;6
                0XF8,//;7
                0X80,//;8
                0X90,//;9
};
void main()
{i=40;
 t=0;
  TMOD=1;//Set timer 0 to working mode 1
  TH0=(65536-46080)/256;//Timer 50ms high 8 bits modulus
  TL0=(65536-46080)%256;//Timer 50ms low 8 bits remainder
  EA=1;//Open total interrupt
  ET0=1;//Timer 0 interrupt
  TR0=1;//Start timer 0
 while(1)
  {
   if(t==20)//50ms interrupt 20 times
   {
    t=0;
    i--;//The total countdown decreases by 1 per second
   } 
   if(i>0)
   {
    p14=0;//Disable the ones digit of the digital tube
    p13=1;//Enable the tens digit of the digital tube
    P0=tab[i/10];//Display the tens digit data
    delay();
    P0=0xff;//Disable the segment selection of the digital tube
    p14=1;//Disable the ones digit of the digital tube
    p13=0;//Disable the tens digit of the digital tube
    P0=tab[i%10];//Display the ones digit data
      delay();
    P0=0xff;//Disable the segment selection of the digital tube
    }
   else{i=40;}
    }
}     
   
void timer0() interrupt 1//Timer 0 interrupt entry
{TH0=(65536-50000)/256;
TL0=(65536-50000)%256;
t++; 
}