I briefly checked out the IowaDNR website http://www.iowadnr.com and didn't see hours listed for the spring turkey hunting, so I assume it is the same for the fall hunt 1/2 hr before sunrise to sunset. In this case there is no night hunting. I have taken birds in the even as they head to their roosting areas, while hunting states that allowed hunting till sunset. I have also takem many birds in the morning. Catching them after coming off the roost, or as they strut with their hens, on their way to feeding or dusting areas.
We also run hunts in Wayne Co, Ia, so if your area is anything like there, I would say that if you hadn't seen anything in the woods where you were set up, I would then move to the fields edges to try to catch them as they are feeding or struting. Not knowing the amount of timber you are hunting it is hard to tell you what you may need to do. In Wayne C0. it is very small amounts of timber in draws between the fields. If it were me I would roost the birds in the evening and once I knew where they were, I would set up on the fields edge near where they are roosting to catch them after they fly down. Anything else, please ask.
Check out the Northwest Turkey Federations website. They may have info that could help you as well.