Open enrollment is a window during which individuals and employees may add or drop their health insurance, or make changes to their coverage. Under the ACA, individual health insurance has open enrollment windows, which apply both in and out of the exchanges (prior to 2014, people could apply at any time, but had to go through medical underwriting).
General open enrollment in the individual market for 2017 coverage runs from November 1, 2016 through January 31, 2017. The earliest possible effective date during that open enrollment session is January 1, 2017.
Individual market open enrollment will follow the same November 1 – January 31 schedule for 2018 coverage, but will switch to a shorter period (November 1 to December 15) for 2018 coverage and beyond, assuming the ACA remains in place.