Has Keyes been in any of the pre-trial hearings to date? I don't think so, since his presene is not required. He can follow the events over the internet, even from a ship. (Although I understand it's pretty expensive), since your wireless link is 22,000 miles up to the switch, and another 22k back down to the wired 'net.)
The cruise was also probably set up before the trial dates were set. Besides, as everyone knows the dates will slip when the government lawyers appeal every decision that is appealable. Starting perhaps with the dismissal of the motion to dismiss, but certainly with any discovery motions and orders. He'll be back in plenty of time.
Somehow, having messages pertaining to Birther delusions transmitted through outer space seems so... apropos.