JNB TF0,$
CLR TF0 ????????
you had better to enable timer 0 interrupt (et0) and run your timer.
place a code to 00b0h (timer0 interrupt code location) ie:

org 0000h
ajmp main

org 00b0h
ajmp t0_isr
...
...
...
org 0100h
main:
; make you timer mode init etc.
...
...
setb tr0 ; run timer0
...
...
...
sjmp $

t0_isr:
; if necessary restore your timer values
; count your 250uS or whatever here
; and check for 1 mS then cpl your pin
...
...
...
reti