Full JB build: 75min
Full ICS build: 55min
Full GB build: 20min
All on same HW: quad core i7 w/ 8GB or RAM, RAID1 HDs.
FWIW, the packaging thing was attempted by Sony-Ericsson: https://events.linuxfoundation.org/events/android-builder...
I lobbied them to open source it but it never happened. I don't know if it would every make it upstream either. By the looks at what happens in the "classic" embedded Linux world (Yocto, Buildroot), it's not like there's a consensus on the use of packages (i.e. lots of people still build from scratch.)