I submitted all of my stuff the first week of November and my final letter of recommendation was received by them on November 11. So it took just over a month. I still haven't gotten anything official from them yet but I've been stalking grad forums from the past few years and it seems the buttons always show up first. DU is my top choice as well so I was checking like every day haha.
Best of luck to you!!! Perhaps we'll both end up in Denver!!!