On eBay, the busiest time of day is from 6:30 to 10:30 in each time zone. Asked if drinking might be a factor, Steve Yankovich, vice president for mobile for eBay, said, “Absolutely.” He added: “I mean, if you think about what most people do when they get home from work in the evening, it’s decompression time. The consumer’s in a good mood.”

Nighttime shopping is growing over all. ChannelAdvisor, which runs e-commerce for hundreds of sites, says its order volumes peak about 8 p.m., and that shoppers are placing orders later and later: in 2011, the number of orders placed from 9 to midnight increased compared with previous years.

A recent array of nighttime offers sent to a shopper’s e-mail inbox included: from 6 to 9 p.m., a limited-quantity sale on fashions at Neiman Marcus; at 7:38 p.m., a promotion for three-day stays at Loews hotels; at 8:44 p.m., a promotion by Gilt for macaroons and faux-fur blankets; and at 2:23 a.m., an offer by Saks for a $2,000 gift card with purchase.

At QVC, the television shopping channel, traffic and viewers rise around noon, then quiet down until after 7 p.m. Then items like cosmetics and accessories sell briskly. “Call them girl treats — they seem to attract a really strong following once you get past dinnertime,” said Doug Rose, senior vice president for multichannel programming and marketing for the company. “You can probably come to your own conclusion as to what’s motivating her.”

Still, the nighttime spike requires delicacy among retailers: for reasons of propriety, they do not want to be seen as encouraging drunken shopping, and many people who inadvertently buy products in that state would most likely return them at high rates. On the other hand, a happy customer can lead to higher sales.

“In a shopping context, alcohol would lift people’s moods and make them feel more relaxed,” said Nancy Puccinelli, an associate fellow at the Oxford’s Saïd Business School who studies consumer behavior. “If we see a product and we feel good, we will evaluate the product more positively.”