Am I qualified for AOTC? I've been on F1 visa and I'm currently a resident alien (>5 yrs). I did 4 years of college and currently in 3rd year for grad school, all in US.

Should I count years of postsecondary education for the eligibility of American Opportunity Tax Credit (AOTC) starting from when I became a resident alient (in my 2nd year of grad school)? In that case, it would be 2 years and I would be qualified. 

Or should I count the years I was in college? In this case, it would be more than 4 years and I would not be qualified for AOTC.