I would run 50 to 60 units max on the frozen ground.  If you have limited tillering, you need the nitrogen there immediately when the weather breaks and who knows what the weather will be.  To boost spring tillering you need a split application.  Nitrogen hungry wheat won’t tiller much waiting into March for an application.  Southern Illinois should be similar to our area.  Assess the nitrogen need for your level of tillers at Feekes 5 or 6 in March and make the second application.