I talked to the shoshone plant superintendent today about what they were doing. He said that they were doing work on the dam and that they were intermittently releaseing water into barrel. He said that there wasn't a schedule to the releases and that there were typically of a couple of hours in duration. He expected the on/off releases to happen for the next several weeks while they do the work.
Sounds like if you are there and its running you can get it, but you won't be able to plan on when it will go.