Actually, I already did (post 26 on page 2), haha - I'm the one who suggested trying to light up the outside of the tank where the tang is acting up.
Possibly - foxfaces are known to be incredibly timid/jumpy. Since you know approximately what time this happens every day, you can watch it to see if you can figure out any correlations that occur at that time (I mentioned the lighting/reflection specifically off the idea that maybe the light - either natural light or the lights over your tank - may change at around that time and lead to the fish seeing its reflection).