AVR Freaks

I'm try to make a delay with Timer.It's build fine but some times its gonna hang and delay time changes.code is following:

/************************************************************************/
//Timer1 Overflow interrupt subroutine
/************************************************************************/
volatile char	Timer1_OverFlow_Flag = 0;
uint16_t		Timer1_i		     = 0;
#define			Time1_Delay		      0.001					
//1 = 1S,100 ms = 0.1 sec = 10Khz,500 ms = 0.5 sec,
//50 ms = 0.05 sec,1 ms = 0.001 sec,0.0005 = 900Hz
ISR(TIMER1_OVF_vect)
{
	
	if(Timer1_i>(Time1_Delay/0.000185))
	{
		Timer1_OverFlow_Flag = 1;
		Timer1_i = 0;
		
		//PORTD ^= (1<<PORTD1);
	}
	
	Timer1_i++;
}



/************************************************************************/
//Configure Timer
/************************************************************************/
void set_Timer1()
{
	TCCR1A  = 0x00;							//Normal Mode
	TCCR1B |= (1<<CS11);// | (1<<CS00);		//clk I/O/8
	//TIMSK1 |= (1<<TOIE1);					//Enable Timer1 Overflow interrupt

	TCNT1   = 65280;						//256
}


//////////////////////////////////////////////////////////////////////////////////
void EnableTimer1()
{
	TIMSK1 |=  (1<<TOIE1);					//Enable Timer1 Overflow interrupt
}

void DisableTimer1()
{
	TIMSK1 &=~ (1<<TOIE1);					//Disable Timer1 Overflow interrupt

}
//////////////////////////////////////////////////////////////////////////////////


int main()
{

	set_Timer1();
	
	sei();						//Enable global interrupt
    DDRD |= 1<<DDRD1;
    
    while(1)
    {
        PORTD ^= (1<<PORTD1);
        
        EnableTimer1();
 			while(!Timer1_OverFlow_Flag);
 			Timer1_OverFlow_Flag = 0;
 		DisableTimer1();
    }
    
 return 0;   
    
}