[edit] you can not edit the title, this is more than 2 things[end edit]

1) you call T1_Start() from two levels - all kinds of trouble can result.
2) how do you plan to hold 34816 in 8 bits?
TH1 = (34816);
TL1 = (34816);

3) cleaner

void buzzer_timer(void) interrupt 3 
{
  T1_Start();  // start timer again
  if (++ticks10 == 250)
  { 
    if (++ticks == 40)
    {
    P2 &= ~0x0C;
    ticks = 0;
    SCON &= 0x50;
    LCD_Flag = 1;
    TR1 = 0;
    }
    ticks10 = 0;
  }
  return;
}

4) Why do you have a return, illegal in an ISR??
5) Why do you make it 2 levels, why not count to 1000 in an int??
6) You may very well never get to both true, VISUALIZE ticks10 goes to 250 without ticks going to 40 and ticks10 get reset -OOPS

Erik