The deadline was supposed to be Monday but the Obama administration extended it by 24 hours because heavy traffic was hampering some people’s attempts to use the site and the administration wants to do everything possible to maximize the early enrollment numbers.
If you want to be covered starting at the beginning of next year you need to choose a plan by the end of today. You don’t technically need to pay the first premium though until January 10th to be covered starting on the first. The insurance industry has given people an additional 10 day grace period for this first month.
Given the system is still experiencing back end problems I would definitely recommend against waiting until the 10th to make your first premium payment. After selecting a plan you should try contacting your insurer to make sure everything is correct.
The open enrollment period goes until March, which is also when the individual mandate penalty starts. So if you are not in a hurry to get coverage you still have another three months to select a plan.
Photo by Ano Lobb under Creative Commons license