Our experience with NYStateOfHealth a few years ago when DH was between jobs is that there are 2 competing calculations the state will want to do. I'd calculated our annual income, and figured that we were eligible for ACA, but the state wanted our monthly income to first determine if we were eligible for Medicaid. If your monthly income makes you eligible for Medicaid, then you are not eligible for ACA subsidies, regardless of your annual income. When your monthly income changes, you might get ACA.
At least in NY, I believe there is continuous open enrollment for Medicaid. Although, there is a lag time before coverage begins: if approved before the 15th of the month, coverage can begin on the first of the next month. If after the 15th, then coverage begins on the first of the month after the next month. So begin the process early!