My take on this is, it's not whether you practice, It's how you pracatice.
I learned that long ago playing golf.
Two things I always tried to do when I went to a driving range:
1. Practice something specific and useful instead of mindlessly hitting golf balls until the bucket is empty.
2. When I'm done, I'm done. When I reach a point where I feel as if I've accomplished what I set out to do, I STOP and walk away even if it means leaving some golf balls behind.
The same thing applies to guitar.
1. I play (practice) something I specifically want to improve.
Take speed for example, whatever I play has to challenge me to play up to speed. Whether it's a slow tune over which I want to play in 16ths or even 32nds, or a fast tune where I have to reach a certain speed in order to keep up, either way I play to accommodate my goal. It doesn't necessarily have to be musical at the outset and may simply involve working on timing, fingering, etc. and the musical part can come later. But the idea is to focus on something specific.
2. I play for as long as I'm in the zone and once that zone disappears (I visualize that as a bubble popping), then it's time to stop and do something else because just as with hitting golf balls, if I keep going and my mind isn't into it then I won't enjoy it anymore and it will likely produce poor results and bad memories. And the last thing I want when leaving a practice session is a bad memory because it tends to overpower any good things I did earlier and leaves me feeling disappointed.
Whether I practice for an hour or longer or for just ten minutes, I want to walk away feeling as if I've accomplished something and feeling good about myself rather than just mindlessly "woodshedding" for hours on end or forcing myself to work on something in which I have little desire or interest at the moment.