I tried the SNS method a couple of times, but was not sure that I was pitching at the proper time, and I didn't see any improvement that seemed worthwhile to me. I was using a 1 gallon plastic milk jug rather than a glass container. Is that OK or is there some reason it is not recommended?
Glass is always better when dealing with cultures because it is easier to sanitize. I do not know where you are located, but most better homebrewing suppliers carry 1-gallon glass jugs. One-gallon glass jugs filled with apple juice can often be found in grocery stores after the apple harvest; however, glass has been replaced plastic in a lot of places. If you are willing to pony up the dough, my preferred SNS container is a 5L borosilicate glass media. However, this size media bottle is not cheap, even used. Here is a photo of my old Corning 1395-5L 5-liter media bottle (I gifted it to a talented young brewer I know when I stopped brewing four years ago):
I generally start brewing around 8 or 9 in the morning and pitch my yeast around 2 or 3 PM. I made the SNS starter first thing in the morning, but that was only 6-8 hours before pitching. To pitch at 12 hours would require me to wake up in the middle of the night to make the starter or delay pitching for hours after I have finished brewing. Neither of those options is convenient for me. If I make a starter ahead of time and refrigerate it then it is one less thing I have to do on brew day and I know it will be ready when I want to pitch it.
You can start a culture the previous day or evening, let it grow for 5 to 7 hours, and then retard activity by placing it in the refrigerater (the culture will still be active, but it will be working at a reduced metabolic rate). The culture should be removed from the refrigerator in the morning as soon as you get up. Placing a starter in one’s refrigerator to retard growth is not remotely the same thing as allowing it to ferment out before storing it in a refrigerator. The cells that are in a fermented-out starter are in a state called quiescence. Yeast cells that are in quiescence have undergone morphological changes where the cell wall thickens in order to prepare for a lack of carbon to transform into energy. These changes have to be undone when a culture is pitched, lengthening lag time.
With that said, 12 hours is not a hard and fast number. However, the starter should be pitched within 18 hours of inoculation for best results, which means that if your brew day ends at 3, you should inoculate your starter no earlier than 9pm (experience with a strain will teach one how early is too early). Retarding a culture will buy one more time, but it takes experience to know when a retarded culture will reach high krausen after being removed from one's refrigerator. In the spirit of keeping things simple, one just needs to be mindful of pitching a starter within 18 hours of inoculation. Also, remember that there are cultures like BRY 97 that take a little longer to reach high krausen because there is nothing average with respect to how long that strain takes to reach high krausen.