I knife cut some late March/early April born calves last night. 10cc of Penicillin just to be on the safe side, and out they go with mama again. Calves don't miss a beat.
I leave them intact until they start to show the first signs of a crest. Heavier muscled calves will crest up before the lighter muscled ones.
Not sure it's the right way for club calves, but has worked for me for years. I do not band ever, though I can see the industry possibly going that way in the future due to animal welfare concerns.