I'm pretty inconsistent these days... But I used to do it a lot, not just daily but for HOURS every day. Again, my form is chanting to a mandala. This is extremely effective-by using a visual focal point, which is what a mandala is for-by focusing your eyes, it helps focus the mind. However-the best meditating I've done, it becomes like a trance-you get lost in it, perhaps impossible to describe, but this is when you can achieve something... I guess it's like watching water boil-I don't believe it happens when you are paying attention like that (by it I mean results). You must get lost in it. By chanting a mantra, which is very rhytHydromaxic, I think it is much easier than silent, or "Walking" meditation, etc. That is just my experience though. But there is no activity more important to me than chanting. But I forget this a lot these days. Some people do this even longer-for as much as even 12 hours at a time, no breaks.
Also-there is definitely a visual effect... that gives you cues, tunnel vision seems common during deeper meditation, as does the mandala shining very brightly... I believe it awakens when your mind awakens if that makes any sense. The whole concept here is FUSION-to fuse your mind with the mandala. And when it does begin to happen-this 2 dimensional object becomes 3 dimensional (and I don't mean like with blurred vision, nor like a hallucination, more like it awakens, or becomes alive), and I've seen it move a bit, shimmer... Hard to describe, and at this point, perhaps it's just too personal, so I'll stop there.
I did want to add one more thing-the sound itself. When you become in rhytHydromax with the ultimate reality (the sound of the Universe if you will), you know it-you kind of hear it, you feel the harmony, the fusion-this is the nature of meditation in general I believe, this is the goal.
Also I wanted to mention lastly-time is irrelevant, it is the nature of how you do it. I've failed for 2 hours straight before, other times, I said the mantra quietly in my head 3 times and BOOM, raised life condition... So I just wanted to add that again, meditation is definitely not about quantity, but quality-and quality is derived from sincerity, but I always wonder what combining sincerity with say, 12 hours would be like-I've never been able to get there, hope I do before I depart this world.