Tony, the same thing happens to me because on the weekend I also shave later - typically late morning. That's about four hours more growth than my weekday shaves. For me, that extra growth makes the shave much more comfortable and closer because the hair is now further from the root and it's softer as well. I sometimes won't show a shadow until late Sunday afternoon from a Saturday morning shave - and I have a coarse, heavy beard. I do take my time on the weekend which does also play a part in the quality shave, but it's not too significant a factor.

Biologically speaking, hair growth is dependant on climate, diet, metabolism, and other factors. I paid attention in my pre-medical classes.

-Rob