I have been training on quickposes.com until its recent demise, and I really learned to appreciate same length sessions. Say 10, 20 or 30 minutes of quick sketches.
I don't like the time schedule you have on predefined lessons, so I started a "same length" sessions, and somehow naively assumed it would end after 20 or 30 minutes. I started drawing, then it turned into grinding and I kept thinking "This got to end sometimes, right?". I finally broke off, and counted 73 sketches I done. That's more than one hour of sketching, without any break, it get's really tiring after a while and at the end the quality started to visibly decline. And it seems for all that I don't even get the cheap endorphine kick of counting this time for practice time on my profile, as I had to break off the session manually.
I would really appreciate that one extra button for the Same Length sessions, that lets me chose after how long a time it automatically ends and counts the time spent towards practice time.