For Pandora, the waits would have to be 20-30 minutes for me to wait. I did River Journey yesterday and visually it was stunning, but quite boring. i have not seen, nor do I have interest in seeing, Avator. So, that could be the problem. A year or two from now, the waits would have to be less than 15 minutes for me to consider River Journey as a standby. I would consider FOP at 30 minutes as it seems interesting and like you need little knowledge of Avator to enjoy it.
I will say that when the new areas at DHS open, I would probably be willing to wait 60-90 minutes.