After my initial use of the Drionic unit I bought back in 2008, I haven't done a full schedule of ionto sessions. As a result, my hands are not as dry as they used to be from the treatments, when I first started using the Drionic.
I'm quite lazy, so I'll do around 4hr's worth of ionto sessions at around 30-45 mins per session, not always consecutively (I'll miss a day or 2 in between sessions sometimes). I almost never do maintenence treatments. I just wait till the sweating gets bad enough that I get sick of it and start the treatments again. I would say I have severe palmar/plantar HH.
Some other observations from the way I do ionto treaments is that my feet used to automatically stop sweating when my hands stopped sweating, even though I've never treated my feet before, but now my feet still sweat a bit even though my hands won't sweat.
Also, the sweating starts to come back sooner then it used to. In the beginning, I went more than 6 weeks I think, before the sweating returned, but now it returns after about a month.
I've probably never done more than 5 hrs of treatments since the first couple times I used it to stop the sweating, so I don't know if the reduction in the effectiveness of the ionto treatments is because of this only, a combination of this and the body building a resistence to the treatments or some other factors.
The most important thing to me, is that despite the reduced effectiveness, which may just be because of my lack of maintenence treatments and shorter total treatment hours before I quit, iontophoresis still works! I'm willing to bet that if I wasn't so lazy, and didn't wait until my HH came back full force before starting treatments again, and did more than 3-5 hrs of treatments at a time, I'd be sweat free to a greater degree and for longer periods.