Hi George. Generally, most of the guided treks in Nanda Devi National Park take atleast 1-2 days. You can join the six days/five night interpretive trek to the Nanda Devi National Park in collaboration with the Nanda Devi Institute of Adventure Sports and Outdoor Education. This will give you a comprehensive tour of the everything that is to be seen in the national park.
If you're looking to visit only for a day, you can stay in Joshimath and visit the park as a day trip. Here are some trips you can check out to know about all your options! Good luck!