Open enrollment for Covered California plans happen once a year. This year this period began November 1st and goes through January 31st.
Generally, you have to apply by the 15th of the month for coverage that begins on the 1st of the next month.
However, for coverage that would begin on January 1st, Covered California has extended their deadline, again. It was to be tonight but checking the website just now, it turns out the deadline is now Monday at 8 p.m.
For more, including hours (They are open today until 6pm PST and from 8 a.m. to 8 p.m. PST) and phone number (800) 300-1506, visit the link below.
Having said all that, keep this in mind. The Monday deadline is only if you are looking for coverage to begin in January. You sill have until the end of January to sign up for coverage that will begin in February or March.
Here is a link to their site. Be careful of imposters, because there are a great deal of them that come up if you search for Covered California.