If it only were that easy. You know how many criminals ask for that (their victims wholly agree) and they still have to go through the whole process whether they want to or not?
That's in a civillian court, not military tribunal.
The German sabatours in WWII caught in the US, for example, from capture to execution, eight months.
And that's with a hang up for the Supreme Court to review the constitutionality, and it was deemed constitutional, almost unanimous. There was a slight dissenting opinion by a couple of the justices on minor details of the wording of the opinion written, not the constituionality of the tribunals.