Prairie Chicken and Grouse shooting hours are Sunrise to Sunset. So no, you do not have to wait until noon on the pheasant opener.
I'm sure you would be fine with Mod/IC. You can always carry the IM choke with you in the field and change if you feel the need to tighten up. If they are getting real skittish you may even want to consider Full. With these choke recommendations I'm assuming you are using Lead. Steel I'd stay with Mod/IC.