I can chainzone across 5 zones with 6 accounts on 3 computers in less than 3 minutes. So IMHO the answer is hardware dependant...
I have buffed many times in GH and chainzoned to where I will camp. When done I will gate back to guild lobby, run to guild hall and rebuff. I am not saying this is a good idea, just that it is possible if your hardware can handle it.
Btw, does anyone know how buff timers deal with lag? Are buff timers counting down in transition between zones?