This type of workout has been around for decades. IronMan featured something similar, based on an article by the magazine's founder, Peary Rader. The program was titled "Add a Half-Inch on Your arms in One Day". The concept was the same: Doing antagonistic supersets for biceps and triceps at the top and bottom of the hour for eight to nine hours. The exercises done at the top of the hour were EZ-Curl Bar barbell curls and lying triceps extensions (French presses); those done at the bottom of the hour were seated dumbbell curls and lying dumbbel triceps extensions.
The rest period, prior to trying this program is three days, instead of four, like that of MuscleTech. IronMan does instruct to rest (no training) for three days, followed by a light training day on the fourth day. The diet portion doesn't go into detail, as does the program described by MuscleTech. IronMan simply recommends six high-protein meals throughout the day (no specific times given). IronMan also recommends rubbing the arms with alcohol, prior to bedtime, after doing this routine.
IronMan claims that this program can be used on 60 to 90-day intervals.
Rader claimed he put on 3/4" on his arms doing it. Old-school bodybuilder and IM writer Gene Mozee said he got 5/8" gain on his arm.
I have actually done the all day arm routine (twice).
The first time I gained (permanently) 3/8" to my arms (I was in full training so it was not after a layoff where gains are easy.
The 2nd time I only gained barely 1/8 of an inch (not even 1/8th of an inch)
Each time I did not do anything out of the ordinary such as massive supplements, eating, or rubbing alcohol, etc.
About halfway thru the day, you start to get worn out by the routine (physically and mentally), but ya just keep[ going.
The 1st time i did it still makes me laugh------I did the routine at home (I have weights at home too), and I remember loading my E-Z curl bar and weights into my van, I had some things to get at the store, and I remember doing curls and standing triceps extensions in the parking lot of K-Mart !!!!!!
The routine has worked for me !!! Good Luck !

P.S. the routine I did was about 8 or 9 hours---it was definitely not a 12 hour routine !