Advice/practice techniques?

So I think anyone's advice can be helpful for pretty much anything, but I wanted to see how other people get started when they practice. I used to run through some finger stretching and picking precision exercises as a warm up for about 15 minutes to a half hour, which is probably longer than I really needed to. I still stick to the metronome for speed developing and generally to play the correct rhythms for whatever I'm working on.
The one thing I do have a problem with is how to budget my time. I do this very poorly, and what I used to do (and occasionally catch myself continuing) is practice the same piece or exercise for way too long (about an hour or 2).

How does everyone else break up their practice time? Do you practice until you're satisfied with your performance (as I have done) or do you time your practice routine, and how would you do so?

These are the things I would like to practice every day, or at least in split-day practices:
Scales and modes
Comping
Chord shapes, forms, and voice-leading
Sweep arpeggii (I think the plural would have an additional 'i'... I need to get back to Italian, lol)
Finger-pickin' licks
Songs and standards

Another thing that I believe has been making this difficult for me is that I find myself either extremely exhausted after about an hour of play or focus and sometimes this is accompanied with one of those "I suck at guitar" kind of moods.. Does anyone have any dieting tips (I know, out of the blue) that could help with my mood and energy?

Anything and everything helps!

=Josh

Oh and I'm an idiot I was going to post a warm-up riff I work on once in a while that might help anyone else who finds it interesting...

e--5-7---6-8-------------
b---6-8-5-7--6-8----7-9-
g--------------7-9-6-8---
D-------------------------
A-------------------------
E-------------------------

etc, etc. Until you get to the 5 and 6 strings, then you reverse the pattern, so:

e--------------------------------------
b--------------------------------------
g--------------------------------------
D-----------------------9---11-8-10---
A---10--12-9---11----8--10-----9--11-
E--9--11-----10---12------------------

You can also vary this exercise using the same fret pattern while crossing strings, so in the first half you would cross from the e to b strings, or e to g strings, etc.