Actually, I have read the label for Round-up, as well as those for generic products with the same active ingredient, and there is no pre-plant interval when using Round-up (glyphosate) alone. As a matter of fact, in many instances you can plant the crop, food plot, hay seeding, whatever, and spray Round-up after planting as long as the desired crop has not germinated. THERE IS NO RESIDUAL SOIL ACTIVITY with these products when used alone.
The only time pre-plant application intervals are necessary with these types of product is when they are pre-mixed with other crop protection products that do have residual soil activity or a potential for crop injury. In those instances the safe interval is dictated by the additional product being added, NOT the Round-up.
No-tilling crops and/or food plots remains an excellent alternative to conventional tillage for small operators where the planting equipment can be rented locally. Many people have a small sprayer capable of the herbicide application if calibrated carefully.
Always read and follow the label requirements for any crop production product. The label is the law!