Probably. Đinner starts around 5pm to 5:30pm, but reservations are needed (not because it's fancy, but because the dining car isn't that big). They take reservations in 15 minute increments.
I have traveled #6 regularly and although not deboarding in Denver, I have always been in the first seating for dinner and finished long before arrival in Denver. Usually they start service right after exiting the Moffatt tunnel shortly after leaving Fraser/Winter Park. I enjoy getting off and exercising by walking all around the Union Station and sometimes up the stairs train side to the pedestrian cross track bridges. Love seeing the full length of the train from above.