I know. But my trip was to Fukuoka and Nagasaki. Hiroshima was the last stop on the way back to Tokyo. The trip's main point was "Southern Japan."

Back on topic, Miyajima is very pretty, but not an entire day's worth of activities, I think. Since you're going in Mid-Feb, you're not going to be able to sit on the beach and sun yourself. That leaves visiting Itsukushima Shrine (where the big orange gate is), Mt. Misen (which may still be inaccessible BY FOOT - the ropeway is running - because of landslides, the Miyajima website has not been updated since November), and shopping. Oh, and the aquarium.

If you were not interested in seeing the aquarium or the mountain (or the mountain is still inaccessible), and you're not going to be there for the Oyster Festival (2/9 - 2/10), you may want to have plans for the later part of the day.