I helped with completely overhauling a UI once. We let people know via email, about the exact date. Then just did it. I voted to keep both the old version and n

I helped with completely overhauling a UI once. We let people know via email, about the exact date. Then just did it. I voted to keep both the old version and new version out for a while, but was over ruled. Rip the bandaid off policy! It actually worked out well.10% will react, but at least you let them know.