Anticipating heavy traffic on the government's health care website, the Obama administration extended Monday's deadline for signing up for insurance by a day, giving Americans in 36 states more time to select a plan.
It was the latest in a series of pushed-back deadlines and delays that have marked the rollout of the health care law.
But federal officials urged buyers not to procrastinate.
"You should not wait until tomorrow. If you are aiming to get coverage Jan. 1, you should try to sign up today," said Julie Bataille, a spokeswoman for the federal agency in charge of the overhaul.
Bataille said the grace period — which runs through today — was being offered to accommodate people from different time zones and to allow for any technical problems that might result from a last-minute rush of applicants.
The HealthCare.gov site had a disastrous debut in October but has gone through extensive improvements to make it more reliable and increase its capacity. The administration said the system was running well Monday.
By the afternoon, the site had received a record 850,000 visits, five times the number logged by the same time last Monday, the administration said. Bataille said the system was handling the volume with error rates of less than 1 in 200 and response times of less than one second.
The Obama administration is hoping for a surge of year-end enrollments to show that the technical problems were merely a temporary setback. That would also go a long way toward easing concerns that insurance companies won't be able to sign up enough young, healthy people to keep prices low for everyone.
But the grace period may be a tacit acknowledgement that the website remains vulnerable to heavy traffic. What's more, the delay offered critics of "Obamacare" another opportunity to argue that the law still isn't working and that President Barack Obama keeps changing the rules.
The administration was careful not to characterize today as a new deadline or an extension, likening the move instead to the Election Day practice in which people who are in line when the polls close are still allowed to vote.
In Pinellas County, the deadline seemed to present little last-minute stress, at least at offices where consumers could seek in-person assistance.
"It's been about average. There hasn't been an onslaught of calls," said Natalie Jackson, who oversees the county government's navigators program. "It's just been the usual flow."
Jackson said the Pinellas offices will be closed today despite the 24-hour extension, in part because there wasn't enough demand for help to justify staying open on Christmas Eve. She noted that people who need additional help can find it on the Internet and through the national hotline, 1-800-318-2596.
In Hillsborough, the Florida Covering Kids & Families program at the University of South Florida had closed down for the holidays and won't reopen until Jan. 2. Callers were referred to local and national websites and the national hotline.
Although 11:59 p.m. today is the deadline for coverage that begins Jan. 1, consumers can continue to sign up for coverage until March and avoid possible penalties for not having insurance. Signing up later simply means that the insurance becomes effective later.
Monday had been the deadline for Americans in the 36 states served by the federal site to sign up if they wanted coverage at the start of the new year. The remaining states operate their own online marketplaces, and some of them have also extended their deadlines.
The president himself signed up for coverage through the government site over the weekend — a purely symbolic move, since he will continue to get health care through the military as commander in chief. He chose a less-expensive "bronze" plan.
Obama said on Friday that more than 1 million Americans had enrolled for coverage since Oct. 1. The administration's estimates call for 3.3 million to sign up by Dec. 31, and the target is 7 million by the end of March. After that, people who fail to buy coverage can face tax penalties.
Minnesota, one of the states running their own insurance exchanges, extended its Monday deadline to Dec. 31 amid problems with its website and extra-long hold times to reach its help center. Maryland pushed back its cutoff date to Dec. 27. New York extended its deadline to midnight today.
Nevada stuck to its Monday deadline, and enrollment counselors there reported a surge of interest.
"We have people lined up out our door. We still have walk-ins. People are asking for help. Our phones are ringing nonstop," said Andres Ramirez in Las Vegas.
In Connecticut, which also kept to a Monday deadline, Ronshelle McIntyre, a 41-year-old mother from New Britain, arrived at a state-run insurance store about 9:30 a.m., and by noontime, she was among about 40 people waiting to speak with a specialist. Some were told the wait could be two hours or more.
"I don't mind," said the mother of three. "For health insurance, I think all it's going to cost me is a little bit of time and patience to get it plugged up, you know?"
Times staff writer Anne Lindberg contributed to this report.