how time consuming is greek life (sororities)?

It's most time consuming during your first semester up until initiation. It wasn't difficult for me to achieve a high GPA. Most houses have study hours a few times a week, rewards for high test/midterm/essay grades, and other motivators to do well academically. On a handful of Fridays, there are philanthropies, and during homecoming week there are events every day. On Thursday-Saturday nights there are parties. There's always something to do if you're looking for it, but I've never felt any pressure to go to an event over studying or anything like that. Look for houses that prioritize academic achievement and have similar goals and I don't think you'll have any problems balancing academics with greek life!