If you release in the afternoon, then the ones that emerged this morning at least will have time to dry their wings a bit. They might be even ready to fly by the afternoon.
Another option is to try to find something else to transfer the other butterflies into until you can release them. Even a large brown paper bag will do. Close the top. This will also give them a bit of darkness until they are released. You might want to add some damp paper towel at the bottom for moisture, but you'd probably need to place the damp paper towel on top of some plastic to prevent the bottom from getting wet and tearing when you take the butterflies to release them.http://www.butterflyfunfacts.com/howtoh ... terfly.php
This website shows how to hold a butterfly with index and middle fingers. This puts less pressure on the wings, too.
Butterflies can also be held in glassine envelopes. The kind that stamp collectors use.