That is great advice. I don't think you can determine the particular time needed to learn. Some people pick it up quick and some others need hours and hours of practice. One size don't fit all here.
One detail I am always tempted to say but have bit my tongue is the detail of the machine. We tend to buy a cheap machine to learn with the intention of getting a better one once we know what we are doing. I did it and regreted it. When I took my first and only FMQ class I had to walk out in tears because my machine was not working well. I could sew a straight line, but no FMQ for me. When I was able to get a better machine (not necessarily more expensive) I was able to do it with no problem. I went back to my old one and no way I could. That only proved that the problem was the machine and not me.
It all started working when I got an older Bernina (An 807 for $100.00 refurbished). That machine still works very well, even though I don't use it much.
What I am trying to say is that sometimes no matter how much you practice, how much you adjust tension, stitch length and your speed, the problem may be external. If you are having problems and have a chance to go to a shop and try another machine, do it. It doesn't cost anything. You may be surprised.