I have attached a link to the Sunrise/Sunset tables for Iowa. Simply select the town closest to where you are hunting and which month and it will give you the sunrise and sunset for that town.
Iowa, USA Locations for Sunrise Sunset Calendar
That should help everyone know what time is legal...
Here is a link to a website that you can utilize to determine the Sunrise/Sunsets during the upcoming season. Just pick what town you are hunting by and what month and it will give you a calendar of that month't times.
Hope this helps some of you.