Thank you for replying, it is good to know other people have picky fish. I also agree, they are mostly active at night for me too!
So, this is really the problem, if I stop feeding bloodworms/hikari, after about a week I am seeing them get skinny again. I would say that I am basing the idea that they aren't eating other things when I am not looking on that. In QT it was a bare bottom tank, so the lack of poop was also an indicator. The one I lost was super emaciated when it died. I feed a few minutes after the lights turn off, as you said, to cut down on the other fish taking food, but guppies... they are a little relentless. No way that a piece of wafer would be left by morning with them. I really have to bury the food or the guppies are getting most of it, and as you said, I don't want to be feeding them bloodworms every night. I could go on like this forever, but once I start traveling for work again this will be a problem. Or maybe not, if they can go 2 weeks or so without food once they are full size.
The tank is right next to my desk, I work from home, and usually in the late evening. So I sometimes watch for hours after I drop food in. They school around, and barble at everything (can barble be a verb too), its totally adorable. My house never truly gets dark, because the 3 adults who live here work totally opposite schedules, so it is possible that has something to do with it?
As for offering the food, I would not feed a day (my thinking was so they were pretty hungry), then keep offering the new food until I thought they were starting to loose weight, usually 3 or 4 days, then chicken out and feed bloodworms. At that time though, they were sooo teeny. I would feel better about going longer now that they are bigger, maybe I should give it another go. It is just the guppies, I love them, but they are little piggies. I should add that when it comes to bloodworms, the cories are not afraid to push them away to get to worms. It is the motivation to get the food first that seems to be lacking.