Shoppers Beware: Deadline for Christmas Eve Delivery Is Quickly Approaching

— -- Christmas is less than 72 hours away and last-minute shoppers aren’t the only ones feeling the heat. Retailers, UPS, FedEx and the U.S. Postal Service are racing to deliver the millions of packages that were ordered this holiday season.

Tuesday marks the busiest day ever for UPS, with 36 million packages delivered to U.S. customers alone, up from 35 million packages last year (a 10 percent year-over-year increase). Among all carriers, more than 960 million packages will be sorted, shipped and delivered this holiday season.

The continued popularity of online shopping has caused retailers and carriers to quickly adjust and adapt to a changing retail environment. According to research firm Forrester, U.S. online holiday sales will exceed $95 billion this year, an 11 percent increase from 2014. Online sales account for 10 percent of overall retail sales, Forrester said.

UPS and FedEx reassured customers earlier this month that their packages would be delivered on time after ShipMatrix, which analyzes delivery rates for carriers, said UPS and FedEx had slower delivery rates for the week following Black Friday and Cyber Monday.

Steve Gaut, a spokesperson for UPS, told ABC News earlier this month that "the vast majority of UPS customers are receiving their packages on time per the scheduled shipping commitments.” UPS said it had hired about 95,000 seasonal workers (drivers, package handlers and delivery helpers) to meet demand. UPS public relations director Susan Rosenberg told ABC News that Christmas is an official UPS holiday and she knows of managers who have made “spot” deliveries on Christmas Day. The company is expected to complete all holiday deliveries Thursday evening, she noted.

FedEx said it’s forecasting a record-breaking 317 million shipments between Black Friday and Christmas Eve - a 12.4 percent hike in seasonal volume from 2014.

Some retailers have already warned customers that their gifts may not make it under the Christmas tree. Jet.com, a 6-month-old start-up that markets itself as a competitor to Amazon, issued a statement on its site that notified customers of a possible delay.

“This year’s holiday gift rush has led to nationwide shipping delays that have affected many of our fulfillment partners,” the company said. “We are committed to creating the best possible experience for our customers, so we wanted to let you know that we can no longer confidently guarantee delivery by December 25th for any items not flagged as eligible for 2-day delivery. Thanks for shopping with us as we go through our very first holiday season. Whether it be this year or next, we hope to see you here again soon.”

The holiday clock is ticking but shoppers can still put off their gift buying a little bit longer before Santa Claus arrives. Better hurry up though -- time is running out.

Here are the ordering cutoffs of some retailers:

Amazon: Today is the last day to get free 2-day shipping with Amazon Prime. Same-day delivery for Dec. 24 is available in 16 metro areas. Customers in these select cities have to order items by noon to receive them by 9 p.m. local time (cost is $9.98 for the first item and 99 cents for each additional item).

Macy’s: Orders have to be placed online by 5 p.m. ET for guaranteed Christmas delivery.

Tiffany & Co.: The luxury jeweler is offering free shipping on all orders and will guarantee Christmas delivery if orders are placed online by 3 p.m. ET on Wednesday, Dec. 23.

Saks Fifth Avenue: Christmas orders have to be submitted by 12 p.m. ET Wednesday, Dec. 23.

Best Buy: If you want that Apple TV for Christmas Day, you need to order by 10:30 a.m. CT on Dec. 22 (today!).

Kohl’s: The discount retailer is guaranteeing Christmas Eve delivery if items are ordered by 1 p.m. CT on Dec. 22. Shoppers will have to pay $29.95 for 1-day shipping.

Walmart: Today at 7 p.m. ET is the cutoff for holiday deliveries. But there are a few caveats: Rush shipping is required (the price of rush shipping depends on the item) and Walmart is not 100 percent guaranteeing Christmas Eve delivery even with rush shipping.

Sears: The standard shipping deadline for orders delivered on Christmas Eve is 4 p.m. CT today, Dec. 22. Some items online can be shipped directly to your local Sears for pickup.