I cannot say anything about how much the queue is indoors since we had FP.
That being said, I wouldn't miss it, as it is completely a thrilling and beautiful experience. I would recommend that if you do not get there for the opening (when it's not an EMH day), that you go on while Rivers of Light is happening. When there is a massive show, or fireworks display in the park, a lot of people are enjoying that. So when there is a a ride I want to go on that has a massive wait I tend to do that.
Peter Pan the other day was well over an hour and when Wishes started, I went on the Haunted Mansion, as well as was able to easily walk onto Peter Pan. It said 20 minutes, but I probably waited less than 10. I cannot guaranteed it would be that dramatic, but I usually have good luck on getting a lesser wait time when shows, or fireworks start. Once again, may not be that dramatic (as while I was at the park the other day it would never stop being under 180), but I would imagine it would still decrease the wait time.