We dined at Whispering Canyons on our check-in day. The PS was for 2:10 and there were a few, but not too many groups seated after us.
My guess is that you would have time to get there in time to eat assuming you have no transportation problems.
We really enjoyed our meal. I had read many reviews that stated that people went for the atmosphere and not the food, because the food was average. I thought the food was very good, but I was somewhat underwhelmed by the atmosphere. It is a beautiful setting but the infamous antics of the servers were few and far between. There were so few people in there that there were not too many opportunities for the cast to shine.
Next time, I will go during a busier time when the atmosphere should be more lively. If you are looking for the entertainment aspect, you may be better off waiting until you have time to go during peak hours.