Here's the national park site if you haven't seen it yet. It has lots of good information. By the way, every national park has a web site like this.
https://www.nps.gov/badl/index.htmTo drive the paved road from one end to the other can be done in 1/2 day. At the west end is Wall Drug for a refreshing drink. :) The park's campground is at the east end of this road.
If you're planning to do the Junior Ranger Program you might already know but they take a lot of time to complete and you should get the materials as soon as you enter the park because a lot of it will be found as you're driving.
You are also planning on at least one hike but perhaps more.
I would recommend at least 2 days if you want to do all of that.
Have a great trip!