The Cutler protocol does state 3 days on before you stop, or at least that that's ideal. Either way, part of the protocol involves waking up at night to take some ALA before going back asleep.
Because of my schedule, Saturday through Monday is the most convenient time for me to be on ALA. See, on Friday nights, I tend to stay up a bit late, and I sleep long, often until 11am or so the next day. Friday is not a good day to be on chelation. On Saturday I can make myself wake up and take it easily enough as a starting day for chelation, and on Sunday, I tend to stay up somewhat late due to it being the weekend, yet I must wake up early because Monday is a work day. So I could easily wake up and take the ALA in the middle of the night on Sunday nights as well. But once the work week has started, it's not worth continuing to do this. I can only take so much of "wake up at night, take ALA, get back to bed" in one week.
So, I'm not going to extend my "on" periods. And having an "off" period that's really short compared to the "on" period, from what I hear that would be a disaster. At least, it's heavily recommended that the "off" period be at least as long as the "on" period. So I don't want to risk it.
3 days on 4 days off does fit both criteria though.