I do it all at the Vet around weaning time. Bangs between 4-12 mos. Vet has a gas brand heater box and outlets for electric brands at his facility that I use. My thinking is get it all done at once saving the time, effort, and stress of running them through multiple times. After all, the vet has to do the Bangs anyway. Too much stress is a big cause of illness too.
I don't know what you have, but I'm assuming you have a trailer to get them there.