Healthcare.gov, the federal Obamacare exchange, is expected to be taken offline for as many as 12 hours during all but one Sunday over the open enrollment period.

The Department of Health and Human Services is planning website outages from midnight to noon every Sunday except Dec. 10, according to slides from a navigator that journalists posted on Twitter. The agency is also planning to take the exchange offline overnight during the first day of open enrollment, on Nov. 1.