When do I release my ladybugs?

I just found spider mites on my plants that are almost ready to be chopped so I don't want to use a bomb and I got ladybugs instead at the suggestions of several people. I have never used them before though and just don't know when to release them. I know when you release them outside you want it to be later in the evening so it's not too hot and they don't just fly away. But what about inside? Maybe this is a stupid question but can ladybugs see in the dark??? Any suggestions would be appreciated!
P.S. What do I do with the ladybugs if they're still alive when I'm ready to harvest? Just try to sprinkle them off onto another still growing plant?