The new online exchange where people can buy health insurance opens Tuesday, but advocates for Wisconsin residents who will be shopping for coverage say Dec. 15, not Oct. 1, is the date that most concerns them. That's the cutoff for coverage beginning in January. The date is especially important for 92,000 people being forced off Wisconsin's BadgerCare Medicaid program at the end of the year. If they don't meet the deadline, they'll have no insurance at the start of the new year. There could be a "big bottleneck" around that December deadline, worries Jon Peacock, research director of the Wisconsin Council on Children and Families.