From the Exit 66A to the Airport Google maps shows 50 Minutes at 59 Miles. The Range is about 20 minutes off the highway, so from the range directly it should be about 1:30 max. It's a straight shot down I-76 and the speed limit is 75MPH. You can easily do 80 on there without an issue.
But it's before Fort Morgan and they have that listed as 77 miles from DIA... you cut off 76 at Barr Lake and it brings you in the back way to the airport.
As I have noted, if you select your flight for 6PM or later you should be 100% okay even being at the Airport 2 hours ahead of time. I suspect the entire event will be finished by 1PM or so on Sunday, if you rushed you could make a 4:30 flight without issue.