I was told that once crabs are out of the water they should stay out. They expend a lot of energy spitting it out so you dont want them having to do that again and weaken them more.
Bad rumor. I have dipped crabs for 25 years and the crabs survive just fine. I just hooked up a washdown pump and hose on my boat this year, so now we just constantly hose them down, and I'll dip them just before leaving. I use the plastic, orange baskets, so I never have to worry about "bottom blowing out". On very hot days, we keep the crabs in the river in a holding pen that I made. We call it "The Condo". Works like a charm.