First - we got lucky and our tour was on a picture perfect day - which are pretty rare in the rainforest of Volcano, HI. Our tour guide Eric made the trip perfect. He has a geology degree and is obviously a student of the volcanoes.
The tour included all of the major stops in the park with a history lesson and tons of information. Almost all of the biking was downhill, so even if you aren't an avid biker you should be able to do it - you just need to know how to ride and be in reasonably good shape.
After the 3 hour tour of the park, they drove us to the sea where we had lunch on the volcanic cliffs overlooking the ocean. It was a great sandwich lunch with wonderful ocean views.
We did the 10:00 tour, which was done by 3:00, then we re-entered the park to hike down the Kilauea Iki trial. We returned at sunset to view the glow coming from the lava inside the Kilauea crater.
If I had one day to see Kilauea, I would absolute do it exactly the way I did it. 10-3 bike tour, 3-5 hike down Kilauea, get dinner, return after dark for the glowing lava.