Gordon Shumway said
I'm trying to get in 3 hours' practice per day, and it's frightening how little you can achieve in that time!

  

@Gordon Shumway 

Do you mean how little you can achieve in your practice?

I have been practicing on average 1 to 2 hours a day.  I can get through all of my material plus play some songs just for enjoyment in that time.  

3 hours of practice can be a lot for some, and not enough for others.  Professional musicians can spend at least that much and more time practicing.  But these are pros that often play in professional orchestras which demand the highest quality performance.

For myself, I have been playing almost 2 years and still feel I am beginning.  My practice time is often limited because I also have a job.  I cannot always find 2 hours to practice.  I do want to practice more, but honestly, I get quite sore in an hour and a half.  When I can, I break it into 2 sessions a day.  This helps, and there is research that suggests that is a better way to practice.

I am curious why you feel you are not accomplishing what you want in your practice?

Are you currently playing in an orchestra?  Is your skill level not where you want it to be?

That schedule sounds quite demanding to me.  Although I have known people who have been at orchestra rehearsals that can go at least 3 or 4 hours.

I do need to put more into my practice, if for nothing else, to increase my stamina.  That alone is an accomplishment.