Of course, the length of your stay depends on the kind of experience you want to have. Some options for your stay in Denali National Park:
Typical Trip: 2 nights
The typical itinerary for those staying at the park entrance is to stay 2 nights. Arrive in the afternoon, with time for an activity like rafting or flightseeing. If you have the energy, take in a dinner theater show or dogsled demo. Then wake up early the next morning and spend most of the day doing the park tour. On the third day, consider an optional activity in the morning before departing around midday.
Kantishna Lodge: 3 or 4 nights
If you don't mind leaving your car and paying a bit more for lodging, you can get a true flavor for the park by going to Kantishna and staying at one of the rustic lodges tucked deep inside the park. This option requires a commitment, because of the 6 hours it takes to bus out to Kantishna, most people go for a few nights or more (air taxi service is also available). The lodge vans to Kantishna leave around 1pm, so most people spend their first night at the park entrance. But you can also catch a 7am coach from Anchorage, which gets you to the park entrance in time to catch the 1pm van to Kantishna.
For those who want to take advantage of more of the activities the park has to offer, spend an extra night. This will allow you to take a full - day raft adventure, to go fishing, horseback riding, or just hike around.