well the time needed to get it all fine and swanky even from stage 3 is going to depend on your hardware
gentoo offer amd, p2, p2-mmx, p3, p4, ppc, alpha, and sparc optimized versions
running a stage 3 p3 optimized version will still take time, but it will basically be the best linux your p3 ever had
run a stage 1 and you are in charge - linux with your own grubby paw-prints all over it