Not knowing your hiking ability, interest in studying area characteristics related to the history of tragic event, desire to linger and enjoy the views, and other factors ... it's difficult to advise you.
However, having hiked it more than once, I would recommend minimun of four hours (pretty much just up, look around, and return). Six or eight hours if you take the book and study the area and event history, have lunch up top, hike over the top, and/or hike down Rescue Gulch. Take plenty of water, as it is really dry up there. If nice weather, plan time to cool off in the river while waiting for boat ride out.
That's just my take, so recon the hike by researching, map recon, google earth, ONX, and whatever to develop your own personal plan. (Ask your boat-shuttle guy, as he may have a good idea based on others' trips.)