This was do-able in WoW 1.x (prior to 2.0 before TBC launch) in just 3 days, before TBC ever came out (not talking about WoW Classic).
A hunter in the guild I ran (we rolled onto a new server) did exactly that. 3 days. I felt bad for taking an entire week to hit 60, when fifteen members (incl warriors) hit 60 in the first five days.