You don't need to feed for 24 hours. Keeping them for 24 hours is recommended to let them dry their wings thoroughly.
You can feed them after 24 hours in several different ways. Offer cantelope or watermelon. Offer juicy, juicy, or honey water or gatorade on a sponge, or paper towel, or q-tip, or tissues. Or, put them into a small letter envelope and put them into the door of the frig in a plastic container for a couple of days to chill them until the weather gets better.
If they are flapping way too much and look like they are going to break their wings, put them into a dark area or enclose the container with a black garage bag.
A clean laundry hamper can be used as an adult container, too.http://www.monarchwatch.org/rear/index.htm