Sounds tight to me. I've never connected from an international flight, but Customs/Immigration dumps you back out into the main terminal. I'm pretty sure that you have to go through security in the main terminal (in other words, there isn't a special line for those coming from customs). On a Saturday, lines *shouldn't* be long, but it's not a super short trip to walk from your incoming flight to customs, go through customs, then walk to security, get through security, and take the train back to the concourse your connecting flight is leaving from.

If there's another flight after the one you want to book, I might risk it. If your connection is the last flight of the day, I probably wouldn't unless you're willing to spend the night in Denver if you misconnect.