I've been doing 20 minutes a day for about a month now. It seems to have start to become helpful in being less anxious for a period of time after, I guess about 2 hours? I think I need more like 30 minutes for it to have real effect but I am liking it. I just sit on a bench and pay attention to breath. That seems to be the easiest way to let thoughts pass. Sometimes if an itch or some kind of pain comes up I just focus on it and don't scratch it/readjust, which seems hard at first but also seems to really help with how effective the time spent meditating feels? Its like a bonus bit of entertainment when doing it...as weird as that seems. Theres also been bits poping up that last a couple seconds where it feels like there is really nothing going through my head, not even the focus on breath. That is weird. Some days it feels like I just wasted 20 minutes and felt nothing or even more anxious but from what I've read thats all normal.
I've also been experimenting with it when biking. I can kind of do the same thing and just focus on my breath while climbing hard for a little bit. Not sure if this is yogic breathing or what, but I can get a lot more air in when really pushing out my stomach/breath into your balls or whatever they say.