I was able to get FP's for the Frozen M&G back in September by showing up about 40 minutes after the park open. That was on a weekday when the park opened at 10am to 8pm. My return time was like 6 hours (4:10 to 4:30pm) after we got the FP's at 10:40am. If you don't get in the queue before or right around the rope drop time, the wait time will be for later that day. I would say the FP's would be gone about an hour to hour and a half when it opens.