The notion that you should schedule your refeed or higher carb date on the day you train your weakest muscle group is something which has been a common approach, and I can see the rational behind it!
An influx of carbs especially when dieting would produce a more anabolic response through insulin, and promoting the pathway that signals growth (AKT) or as we may be familiar with the term muscle protein synthesis.
It makes sense that taking advantage of this “spike” on your weaker body parts, but as we know muscle growth does occur over night nor are we likely to grow in a deficit.
How you want to structure your refeed day I feel would be more beneficial on your leg or back days (bigger muscle groups), allowing you to have more fuel to train harder. If your bigger muscle groups just so happen to be legs or back then it’s a win win 😂
If anything your refeed on weaker muscle groups will allow you to train it harder, which could ultimately lead to more muscle retention when dieting down. Personal preference will come into play with where you want to allocate your refeed.
If I wanted to have the best session possible for legs on Friday, scheduling my refeed on the Thursday to allow enough time for my glycogen levels to be replenished May be the best approach.