Pretty sure you don't have to worry too much about doing a gradual switch of dose times with Vetsulin-- it's an "in and out" insulin, so if you move the shot earlier you just want to be sure the previous shot is out of the system. Given that he's spent the day in pinks and you gave a reduced shot this morning, I think it might even be fine to just go back to your regular time in one shot, though as usual I defer to any experienced Vetsulin users who might disagree with me on this. If you are nervous about doing it in one step, maybe an hour earlier on tonight's shot and the second hour tomorrow, whenever works for your schedule and depending on his numbers.
Some of the earlier, more complicated, discussions may have come about because the people commenting had used Lantus or another "depot" insulin-- those are much less forgiving about changing times and have to be moved very carefully, 15 minutes per cycle.