I have been using the shirakura pellets and powder for over 2 years and all my CRS love it. The reason you raise the air when feeding the powder is because if you don't it will just float at the top. This is fine for the larger ones that actually go to the top and turn upside down and feed, but I have noticed most of my new born shrimp won't do that so you have to get the powder to sink and spread around or they won't get any food. In the 2 years I've had mine I've gone from 10 to over 200+ and have only noticed a couple of deaths so far. So I would say shirakura is a no brainer. I however only feed them once every few days to ensure a healthy appetite. You don't want fat lazy shrimp now do you?
Should I get Shirakura food for my RCS? Right now I feed crab cuisine, shrimp pellets, Hikari algae wafers, blanched zucchini, and occasionally Hikari tetra micro pellets. Everybody seems happy and I've got lots of berried, saddled, and a few berried and saddled females. Just wondering if I could be feeding them better or not.
Sounds like you have a well balanced supply of food for your shrimp. Sure, try it if you want but it is not a must for you. I also have different foods for my shrimp and they were healthy and happy but I just wanted to try the Shirakura food and the shrimp still seem happy and healthy.
You can leave it there as long as they are still eating. If they aren't eating it, you should remove it after 2 hours. Shirakura food is stable and will barely affect water quality if left for 24 hours.