I caught a few shiners in a river by my house, water temp of around 50-ish.
Dripped them for an hour-ish, bucket was 1/2 tank water and 1/2 river water so it warmed up a fair amount. However the second they hit the tank, DEAD. They don't do well with huge temp changes in short times it seems, well at least in my experience. Same with Rosys, I can only put them in as fast as the fish can eat them because they are dead less than 10 seconds after they hit the water from the heat.
Dripped them for an hour-ish, bucket was 1/2 tank water and 1/2 river water so it warmed up a fair amount. However the second they hit the tank, DEAD. They don't do well with huge temp changes in short times it seems, well at least in my experience. Same with Rosys, I can only put them in as fast as the fish can eat them because they are dead less than 10 seconds after they hit the water from the heat.

I didnt miss that part. i just ignored it because it was pointless. You'd be better off setting up a quarantine tank specifically for your feeders. dripping them using the water from your main tank will provide no results since you're trying to acclimate native bait fish that prefer cold water to your warm tropical water. The person who gave you that advice obviously pulled it straight out of his you know what.