Online shopping can be just as hectic and frustrating as in-store shopping the day after Thanksgiving. Shopping on Black Friday, and now Cyber Monday as well, is all about beating the clock.

Nearly a third of shoppers will do 75% of their shopping online this holiday season, according to data and analytics company Zeta Global and market research firm The Relevancy Group, which surveyed 1,000 people.

“If you really are trying to look for deals, you have to be opportunistic and know the deals won’t last long, and to jump on them when you see them,” said David A. Steinberg, co-founder and chief executive of Zeta Global.

See: What to buy, and skip, on Black Friday

Surprisingly, not all Americans feel obligated to shop during the weekend of Black Friday, a survey of 1,000 adults by personal finance website Bankrate.com found: 53% of people said they do not plan to shop on Thanksgiving, Black Friday or Cyber Monday. But 36% said they plan to shop in-store, online or both.

“Black Friday was the main day, then it moved to the week, then month or longer,” said Mike Cetera, a personal finance analyst at Bankrate.com.

See also: Why Black Friday sales are not for the truly frugal

Still, there is no doubt time will be of the essence to catching those holiday deals. Though deals are live throughout the rest of the holiday season, retailers have been furiously pushing out advertisements and commercials about their doorbuster sales for Black Friday.

Here’s how not to miss out:

Check back early and often

Online bidding site eBay EBAY, -0.55%  plans to have a countdown clock on its home page for when buyers can expect to see new deals, said Jesse Kiefer, director and general manager of eBay Deals, adding that many deals eBay and its competitors run are for a limited time. Also be aware of just how many deals there are — eBay, for example, will be launching deals every hour on Black Friday and again on Cyber Monday. Amazon AMZN, -0.66%  launched a Black Friday Deals Store that will feature new deals every five minutes from now until Dec. 22. “On Black Friday and throughout the peak period, retailers are offering the very best deals on the internet,” Kiefer said. “Many products do sell out in a matter of hours or days so certainly if a buyer sees a deal and has the opportunity to buy it, they’d want to jump on it.”

Set a budget and don’t jump on just anything.

Sometimes, deals bring out the worst in us — and we’ll jump even if we don’t necessarily need or want the product being offered. “Make sure you are rational about what you buy,” Steinberg said. He suggests setting a budget, understanding what you want to spend per gift or product and following it. If you don’t need the product for any holidays, consider holding out for when it may be even cheaper. For example, winter clothes are less expensive a few weeks into the season so if you don’t necessarily need that winter coat, you could get it for a few dollars less down the road.

Look for the hottest items — with an open mind

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