I got my first invite (CWRU) 7/20/2017, my second (University of Michigan 😍) 9/14/2017, and my final interview (from U of Colorado) 11/20/2018.
Once you get the invitation they will let you know what dates are available. Interviews usually take place ~3 or 4 weeks after the invitation has been sent out. Hope that helps!
Edit: These were the days when I received the invitation to interview. Not the dates of the interviews themselves*