We did it last year and had a great time.
Your experience may depend on the type of rider you are. There were the racers who finished the daily route before 11am. The were the average folks who stop at every town and enjoy the food and activities (lots of farm animals to be petted!). They would typically arrive between noon and 5pm .The majority falls in this category. And there were the partygoers that would leave late and arrive late, usually happily inebriated
Few things I noted:
1. Whoever said Iowa is flat must have never visited Iowa. Coming from Chicago there was significant (but doable) elevation difference.
2. You never ride alone. The constant stream of riders was amazing.
3. Iowans are very friendly folks.
4. The good pie sells out quickly