Russ, the code will cause both LEDs to be on at the same time, even if the LEDs are referenced to ground.
GPIO.0 and GPIO.1 are the same level in the “second” and the “forth” time increment.
The previously attached waveform drawing shows this.
http://www.picbasic.co.uk/forum/atta...1&d=1178466510
You may have forgotten 4.168 milliseconds is one quarter (“one quadrant”) of a full cycle (16.667) – not one half.
-Adam-