Morning--you pay for the day, so the earlier you get there, the more runs you can go on.
Raft trips go out 2-3 times a day. Tubing I believe is all day, but the guided raft and duckie trips are a scheduled single event. And regarding it being a "float" per what is apparently a tourist, and not completely familiar with the Shenandoah and the Potomac's unique split personality, at low water, it is very technical but not large, if the 'Doah is above 6 feet it really opens up and the chunder comes out. The Potomac is similar, and is a lot of fun above 10'. It depends what the river is doing at the time. Not all rivers are dam released and consistent like the other answer seems to imply.
Morning is good, but expect more of a float down the river. There is very little adventure and few areas that i would describe as rapids.
Early to get more rides.
Morning before the sun gets hot...then settle down for some beers ;)
Mornings are good.
Thanks! Your answer is awaiting moderation.