I've been doing a half hour a day for the last 14 days (which it just reminded me of, as I haven't done it yet today, doh, had a very busy day, so now I have to do it before I go to bed.)
Love the app.
For websites, I prefer memrise, but Duolingo's app is so good that it's basically all I'm using now.
Also on Spanish, and after 7 hours (30 min/day x 14 days) I am just a little ways into level 8, at 1185 skill points, 430 words.
Also just FYI, cause it took me a bit to figure out and everyone I mention it to doesn't seem to use it - swipe right (or click the menu in the upper left) and click "practice" - it'll practice everything you've learned so far.
I normally start my half hour session with 1-2 practice rounds, then do 25 min or so of learning new material, then end with a practice round.