Black Friday's round-the-clock sales apparently were just a warm-up for the homestretch of the holiday season, as many retailers will open their doors this weekend and keep them open straight through Christmas Eve.

In an unusually short shopping season and with just five days till Christmas, retailers are pulling out all the stops.

"It's crunch time, " said Jamie Gutfreund, chief strategy officer at The Intelligence Group, a business research firm.

For the first time, Kohl's will stay open 108 hours starting at 6 a.m. Friday as "an added convenience to shoppers," said spokeswoman Jackie Kacala. Some Macy's stores will log 107 hours of nonstop sales before closing at 6 p.m. Christmas Eve.

And Toys R Us, which has helped pioneer extended holiday hours by shifting Black Friday sales to Thanksgiving, will offer 87 consecutive hours of shopping, opening Saturday at 6 a.m. and staying open until 9 p.m. Christmas Eve. The retailer's flagship store in New York's Times Square has been open since 8 a.m. Dec. 1 and will stay open for 566 hours -- the store's longest stretch of uninterrupted shopping.

"It's been an escalating progression," Gutfreund said. "Ten years ago it would have been 'Oh my god,' but now it seems to be not such a leap. ... It's all about the consumer now."

The shopping all-nighters started on Thanksgiving, when more stores than ever before opened to lure shoppers away from the dinner table and into the malls for sales that used to start on Black Friday. Retailers hope the extended hours will make up for the six days they lost this season; Thanksgiving fell late this year, leaving just 26 days until Christmas and setting up for the shortest holiday shopping season since 2002.

Many retailers depend on the holidays for up to 40 percent of their annual sales, and chopping almost a week out of the season could cost retailers about $1.5 billion in sales, according to a study by Adobe (ADBE) Digital Index.

"These final days are really important to the retailer," said Vera Gibbons a financial analyst and spokeswoman for Capital One. "This is it. This is make it or break it."

It's not just the marathon hours that will feel like round two of Black Friday -- retailers will also dangle sales and promotions in front of consumers, many of them as good as or better than Black Friday deals. Toys R Us is offering 50 percent off and buy-one-get-one deals, with a two-day sale starting Friday. Kohl's is offering cash back on purchases and Target has discounts of up to 60 percent, and has extended its in-store pickup service for online orders to 2 p.m. Dec. 24.

Experts expect consumers will hit stores at every hour of the day and night until Christmas. While retailers have struggled with the shorter season, so too have shoppers struggled to find the time to buy gifts.

"The next (week) will be extremely hectic and busy, and you'll see a huge ramp-up," said Michael Niemira, chief economist and director of research at the International Council of Shopping Centers.

According to a survey by American Express on Dec. 6-8, about 21 percent of consumers hadn't started their holiday shopping yet, and almost a quarter were only halfway finished.

The longer hours also are a response to growing demand from consumers to buy what, when and where they want, retail experts say. Many consumers, especially millennials, expect the same from brick-and-mortar stores that they get from online shopping, which is at their fingertips 24 hours a day.

"Everything is fluid," Gutfreund said :"If I could have extraordinary at a click of a button, I had better be given extraordinary in the store."

Many of the shoppers expected to be out in the wee hours will be the usual procrastinators, experts say, but the round-the-clock hours also give nurses, truck drivers and others who work night shifts some of their first shopping opportunities all season.

Cathy Camp of Lake County was in Emeryville on Thursday to visit family and buy gifts for her grandchildren at Toys R Us. She has no plans to return to the store for any middle-of-the-night shopping, but said the extended hours could come in handy for working parents.

"Once the kids go to bed, one parent could go out shopping," Camp said.

Macy's "extended hours are a direct result of customer feedback," said spokeswoman Megan Pardo. "Our customers asked for more store hours in the day and night to shop, and we listened with stores staying open late at night or opening early.''

But some analysts warn that hitting the stores in the middle of the night with just a few days left before Christmas, when many consumers are tired and overwhelmed, is a recipe for overspending.

"If you're shopping at 4 a.m. people just discount it," Gibbons said. "It's like it's not really happening. But it is, and when you get that bill you'll see it."

It's a tradition that's probably here to stay.

"They've opened up Pandora's box. How do you take it away?" Gutfreund said. "People will accept that this is business as usual."

Contact Heather Somerville at 510-208-6413. Follow her at Twitter.com/heathersomervil.

Retailers' marathon hours
Stores open around the clock:

Macy's
Locations: Union Square in San Francisco and Westfield Valley Fair in Santa Clara
Hours: 7 a.m. Friday to 6 p.m. Tuesday

Toys R Us
Locations: Most stores except for Toys R Us Outlet and Express stores. Toys R Us has more than 20 locations in the Bay Area.
Hours: 6 a.m. Saturday to 9 p.m. Tuesday

Kohl's
Locations: Dozens of stores throughout the Bay Area
House: 6 a.m. Friday to 6 p.m. Tuesday

Stores with extended shopping hours:

Target: 8 a.m. to 11 p.m. though Monday, except closing at 10 p.m. Sunday. On Tuesday, 7 a.m. to 9 p.m. or 10 p.m., varying by location

Kmart: 6 a.m. to midnight through Monday, and 6 a.m. to 10 p.m. Tuesday

Nordstrom: Varies by store, but many open 8 a.m. to 11 p.m. through Monday, and 8 a.m. to 6 p.m. Tuesday