<< The directions are retarded in the first place. There's only ONE reason that man was prohibited from gonig to the bathroom - paranoia. To hell with the air marshals. >>
Have you ever flown in an airplane? As I said before: You are ALWAYS asked to remain seated and wear your seatbelt during descent (and ascent, too). The time period was extended to 30 min because of paranoia, but 15-20 min prior to the end of the flight it STILL always happens.
The reason is for SAFETY. During ascent and descent, the plane is not flying level and the pilot is banking and the plane is subject to more turbulence because it now must pass through cloud cover and atmospheric disturbances which cause more turbulence than normal. Basically, they don't want you up and about where you fall, be thrown, or be hit by flying objects should the plane shake or dip.
Again, passengers are always asked to remain seated at the end of the flight and it's not a whole lot to ask for an adult to sit tight for 30 min.