Suggestion: Infinite practice mode
This is based on an idea from a post I saw earlier.
It would work like this:
Start with 30 seconds
Get one question right: +1 point (+5-10 seconds depending on sentence length)
Get one wrong: -3 points
End if getting to either 0 points or 0:00 time
Last as long as you can!
Thanks for being awesome Duolingo!
Would you start with a certain number of points? As your suggestion stands, if you get any of the first four questions wrong that's the end of the round. Also, would these points be the coins that you would win, or would that be something separate? Personally, I would hate if I could actually lose points toward my language level by getting a question wrong (especially since about 80-90% of my "incorrect answers" are either typos or Duolingo not accepting a correct solution), but I also think that it would be a hassle to deal with counting how many coins you get and how many points you have as well as the time remaining.
Despite all of my objections, I would love some sort of an "infinite practice mode", especially since I've often found myself at the end of a timed practice on a roll with a minute and a half left on the clock, and when that happens I wish I could keep on going and see how long I can last (or how high I can make that time go. Bonus trophy and lingots if you can make your time remaining go above 10 minute? :P ).
I get your issue with the first four questions that also might be the last. The intention is exactly what you describe in the second paragraph: Getting to work on Timed Practice for longer.