As with everything, speed comes with experience. When I frst started LFS it took me many months to get the first LFS book released. Now that I'm a veteran I can build LFS systems in about 1 to 2 hours time depending how fast the machine is in compiling.
You'll spend a lot more time after you finish with the LFS book. The fun only starts then, when you install all the other software that you need such as XFree86, desktop managers or whatever else you want to be using.
Expect to be busy for many weeks to come fine tuning all your software, figuring out how to install it all (do checkout http://hints.linuxfromscratch.org
for helpful information).