I was at a dinner with one of the muckety-mucks from DEN and that was one of the questions. My memory was that DEN doesn't have large issues with customs except when the BA and LH land nose to nose on Saturday. They want to expand Concourse A to accept more international flights and expand customs accordingly. The issue is our federal government which takes forever to do even the most common sense items. Short answer, hope for under an hour, expect 2.