Can one advance in non-timed practice?
Yes - I've only used non-timed practices in French. I'm finished the tree, am at Level 22, and have a high fluency rating (whatever). I like to do timed practices because you earn XP points faster, but when I tried it with French I ended up only earning 3 or 4 points because I'd make so many mistakes or run out of time. I'll move to timed practices when I feel ready.