Playing in "the zone"
For me, playing in "the zone" implies a certain kind of detachment.
When I'm not in the zone there's a lot of self-evaluation regarding how well my execution matches my intention. I can play through the inevitable disappointments, but they're distracting. When I'm in that frame of mind it's difficult to establish any real "flow"; I tend to lean heavily on practiced parts and motifs.
When I am in the zone it's as if every note (and for me that implies voices within a chord - I play very few single-note lines) implies more possibilities. I move to one of those possibilities without planning, and accept the consequences without judgement. Some of the moves are a result of practice; others are intuitive. When I'm playing like this it's almost as if I'm hearing someone else play. Rather than thinking "damn, that's not what I wanted to do" or "yay, I nailed that one" I think "gee, that's interesting... I wonder what's next". Sometimes this flow will last for a handful of notes. Other times it'll last for minutes. The longer I play in that state, the easier it is to get back to when I lose it. It's almost always some non-musical distraction (fatigue or interruption) that finally terminates the flow.
It's most difficult for me to establish flow when I'm playing for other people. There's that voice that keeps asking "is this OK? Do they like it?" Being in the zone is almost a meditative state; boisterous outbursts and presence of friends and family all tend to distract me.
It's a bit less difficult to establish flow when recording. In that situation the voice asks "do I really want this on tape?" There are also technical distractions in the studio. My best musical results come from simplifying my workflow to the point where I don't have to think about it at all, and quickly entering the mindset of "I don't care that a recorder's running, I'm just going to play whatever falls under my fingers."
I don't keep a log, but I'd estimate that I practice about 5 to 7 hours a week - when I feel like it. In other words, it's not every day or every week that I practice. Sometimes I'll take a break because I feel that I've been neglecting other areas of my life or because I just don't feel like there's anything I want to play. When I practice, it's with the intention of making music. I'll repeat parts to get them "locked in". I'll work on conceptual material: chord construction, fretboard layout, etc., but always in some musical context; never for the sake of doing an exercise. I realize that there are limitations to that approach (speed and ability to effectively communicate with other musicians foremost among those limitations). There are also benefits: I play exactly what I want to play and I learn a lot of interesting stuff serendipitously.