Read timer values with C-code

Hi.

I am a beginner with the 8051 controllers, and are trying to run a servo. I need 20ms period and 1-2ms pulses, as Im sure a lot of you guys know.

I was trying this :

void main()
{
uint16_t value = 0;
P0DIR = 0x00;
P0 = 0x00;

TCON |= (1 << 6);         // Start timer 1
TMOD |= (2 << 4); // mode 2 - auto reloads

        while(1)
        {

                if(TF1 == 1)
                {
                        value++;
                }
                if(value >= 26500)
                {
                        P00 ^= (1 << 0);
                        value = 0;
                }
        }
}

calculating that my 16MHz clock is divided by 12 for the timer; 16MHz/12 = 1.3 MHz => T = 1/1.3MHz = 7.5*10^-7 per count.

Then I need 20ms/7.5*10^-7 = 26666 overflows to get my 20ms output. The problem is that this is not quite accurate, it gives about 35ms.
Is my calculations wrong?

Also, I should not be toggling, but that is ust for testing purposes.
Using nRF24LE1.

Thank you all in advance!