Just to be extra cautious, I would ignore the first day on 0.75U and start a week's count from 8/29 and reduce from 9/5 or even 9/6. If he doesn't drop below 50 before then.
Take the full 0.25U reduction. If it fails again and you have to go back to 0.75U (hopefully not), then you can try a dose in between (which is very hard to measure consistently without callipers).
His numbers are looking better this time around on 0.75U - less blue, lower nadirs. Paws crossed that the reduction will be successful.