more like “make -j4 -k check” and chill

It will take atleast 12 hours just to build the LFS in one sitting on a machine that has a 7th gen intel core i5 processor, 4GB of RAM and a 5400 rpm hard drive including typing / copying time.

A system with a Higher Processor, More RAM and SSD will significantly take much less time to complete.

And

Add some more days which will be taken to complete the development of the OS according to your taste using the BLFS book and what you expect your os to do so the time varies for the development of BLFS.