Would being in the US 4 months out of the year be sufficient for applying for citizenship?

My parents entered the US as permanent residents on 12/13/16, their green cards arrived in the mail yesterday. I know that they need to be in the US for more than half of the 5 years before they apply for citizenship, they are planning to come to the US 2 times a year and stay for 2 months each time. They will move here the last 15 months before they apply for citizenship.