Marketers are posting online videos, photos and messages late at night, tailored for phone addicts who wake up in the wee hours and check their social media. "It reminds me a lot of the advertising that you used to get sold on traditional TV on overnight," says Laura Beaudin, a partner in Bain & Company's Customer Strategy & Marketing practice. "If you're up at 2 o'clock in the morning because you can't sleep, that is all you're doing. You're not doing stuff with your kids at the same time or making dinner at the same time, you're a bit more of that captive audience."