For Federal Tax Law, the important question is, "which parent did the child live more than half the nights of the year"? It can't be 50/50 in a year with an odd number of days, and the IRS does not follow custody orders, only where the child actually spent the night. The nights do not have to be consecutive.
Turbotax deals with this question by asking you to estimate how many months the child lived with you. For example, if the child lived 2 nights a week with one parent and 5 nights a week with the other parent, the parents might approximate by picking "3 months" and "9 months" in the interview.
As long as your child lived with you more than half the nights, it doesn't matter if you choose 7, 8, 9, 10, 11 months or the whole year in the program. All are treated as "more than half". Likewise, if the child spent the night in your home less than half the nights of the year, it doesn't matter if you choose 1, 2, 3, 4, 5, 6 months or never. All are treated for tax purposes as "less than half."
