Updated

Secretary of Health and Human Services Kathleen Sebelius has touted "dramatic" improvement in the federal health exchange website since its flawed rollout, but is advising potential customers to use the site during "off-peak hours" as she warns it will not work smoothly for everyone.

In an opinion piece published Monday in USA Today, Sebelius says that Healthcare.gov "is now working smoothly for the vast majority of users." However, Sebelius warns that "there will be exceptions, and (as with any website) we will continue to make improvements."

Later in the piece, Sebelius tells those Americans who have had issues with the site to "please do not give up. There is help available," before giving the number for the site's call center. The secretary also advises browsers to visit the site in the morning, in the evening, or on weekends when there is less traffic. She also touts an online queuing system in which users can elect to have an e-mail sent to them when less traffic makes the site more manageable.

Administration officials said early Sunday that they have fixed roughly 400 computer “bugs” and increased capacity so the site can now handle more than 800,000 users daily with an error rate of less than 1 percent.

Jeff Zients, the White House official appointed to fix the ObamaCare site since its disastrous Oct. 1 rollout, said it is “night and day from what it was.”

Julie Bataille, a Centers for Medicare and Medicaid Services spokeswoman, said the site is “vastly improved,” compared to where it was five weeks ago. Still, both acknowledged more work needs to be done now that the administration’s self-imposed, Nov. 30 deadline has passed.

“This is not a magic moment,” Bataille said.

Officials also said the site can now handle 50,000 users at once and has about 90 percent stability. Congressional Republicans said that the site was still not up to standard, with Michigan Rep. Mike Rogers saying "It still doesn’t function right ... The security of this site … doesn’t meet the minimum standards of the private sector.”