Tours depart at 8am from the main wharf and return at about 4pm. There are numerous identical Dragon boats that all depart at the same time. You can be picked up from your hotel for no additional charge.
The trip visits Linh Mu (Thien Mu) pagoda, Hon Chen Temple, Tu Duc Tomb, Minh Mang Tomb and Khai Dinh Tomb spending between 45 minutes and an hour at each stop. This is definately not enough time for a true temple junkie but it is a good way to get your bearings as to the historical sites in Hue.
Both Tu Duc and Khai Dinh tombs require a moto-taxi once you get there, and the drivers are quite notorious for doubling the negotiated price for the return trip. Each site has an entry fee of between AU$1.50 and $4. Having paid $2 for the boat trip is hardly cause for complaint. A basic cooked lunch is included in the price with the option of paying for extra dishes. The boat itself is basically a decoratively covered barge with plastic garden chairs there is no commentary or guides at the sites.
My advice would be to buy one of the locally produced books before you set out. Many of the sites are just beginning to undergo rejuvination but the sites are truly amazing, in parts faded beauty but grand none the less. Being out on the Perfume River is a trip in itself. The sights and sounds of a working river are well worth the effort and the $2.