metzer said that 14 days rest stuff at the end when he was kinda nuts, I wouldn't look to much into what he was preaching the last few years he was alive.
7 days, 10 days, 14 days or not - the formula is still the same - the more intense, the bigger need for rest, the bigger the rest the less days you can work your body and the less you work your body the less chances to build muscle.
UNLESS of course you can build more muscles by working your muscles every 7th, 10th or 14th day than every OTHER day.
which i do not believe.
especially since that hardcore approach sooner or later will cause you injuries, problems with your joints, fucking up your immune system making you sick etc which will set you back even MORE days in a year.
so do the math.