Why not set the timer to 1ms

DEF SEG = 0
IH = 46: IL = 157
OUT &H43, &H34 'set timer to 1 ms
OUT &H40, IL
OUT &H40, IH
POKE &H46C, 0: POKE &H46D, 0 'zero timer
WHILE PEEK(&H46C) < 2: WEND 'synchronize

DO
POKE &H46C, 0 'zero timer
WHILE PEEK(&H46C) < 1: WEND 'wait 1 ms
'do output here
LOOP