I'd either weigh once a week or twice a week. If the pred is working you should see him gaining very soon (within a week) , even if its only a few ounces at the beginning. Good about the scale, good luck and stay in touch.
Good idea @StephenQ ! I had the same one picked out at Walmart so will get it tomorrow. Of course as an anxious mama we want to know every hour, but that does us no good. Ideally, how often should a kitty like this be weighed? I really feel like he looks thinner in recent days but I could be over analyzing and also he is shaved from the ultrasound. I do feel his spine though.