It depends on your conditions, Ron, but we found we could run another hour or two at night with the draper. Eventually, you will be limited by gound conditions or power as the stems get tough...but the draper will still be feeding evenly. They aren't a perfect cure-all but they sure do make the day go smoother.

[edit to add:] As I said, ground conditions can shut you down for the evening. Leaves on the ground get damp and can start dragging, as with any auger header. With a draper head, though, you can make a slight change to cutterbar angle and keep going. Again, they aren't magic, but they are an amazing improvement. Demo one -- but be prepared to buy!