When I was in college I had to practice about 2-3 hrs ... just trying to make it in. That was with a full course-load and work study.
When I got out of college I was bored so I barely practiced. There was no need to learn all of that classical literature if I wasn't going to be giving any concerts.
Now that I'm out of my element I practice a WHOLE lot (now I have to play chordally, without music, a lot more ear involved). At least 1.5 hrs a day. But I don't time it. I decide what I'm working on for the week and sit there until I get to a point where I have progressed more than the day before.
So, I think it depends on where you're at in your life and if you're in a season where you're learning something new or if you're playing the same old stuff that you already know. It also depends on if you have a day job or not.
But whether you work or not I think a half hour every day is better than 5 hours once a week. It takes your mind time to let things marinate and that's only done with consistency.
I start with finger warmups for technique. After that I practice progressions - T-Bone gave me some new ones. Then I choose a song or two to learn without music. That's my new thing is playing without music so I'm working mostly on that.
I always have to remember that practicing means that you're working out difficult passages for accuracy, otherwise you're just playing.
