I wouldnt go for more than a couple hours after they are killed. They decompose fast. You can put them on ice(live) with good drainage and they will go dormant, they look dead but don't hang like a wet rag. They will last a day or two like that.
Leaving them in the trap is a good idea as long as they don't figure out how to get out.

Crabs are a heck of a lot smarter than a lot of people give them credit