I was experiencing very lengthy install while upgrading my Mac mini 2011 from 10 find out here now.9 Mavericks to 10.10 Yosemite Developer Preview. The install process just appeared to hang at “5mins left”.
After some research, I believe that the cause of this is the MacTex library. If you have installed the MaxTex or any Tex library, you may experience this. The solution is just to wait, it may take a good couple of hours. Leave it overnight and it should be ready the next morning 🙂