> Whether this scheme constitutes obstruction of justice, I have no idea.

Not a lawyer but...

Courts seem to treat programs as proxies for their owners so if it's a program actively doing some kind of destruction then it probably would be. If you could ensure passively, that the data would become unusable after a certain time period it wouldn't.

A physical example would be an briefcase rigged with small explosives. Opening it without the code or waiting to long to enter the code would trigger it to destroy the contents. I imagine this would be considered willful destruction of the contents. On the other hand, if the materials inside could decay into ash in a short time peroid, then it's not willful destruction.