Forever, no! Sure, compiling Firefox with some flags on my slow system can take ahem, time but I can install Gentoo in couple of days.
Though, in all seriousness, Gentoo takes a notch higher than Arch and unlike Arch, which has many entry level distros based on it, Gentoo has comparatively lesser. It’s fully usable but takes some initial time configuring and setting up the system exactly to the user’s requirements. The package manager is portage, I think.