In U.S. v. Ferebe, the Fourth Circuit in an opinion by Judge Luttig joined by Judge Michael held that the defendant facing the federal death penalty could take a collateral order appeal of the timeliness of the notice in advance of trial from the U.S. Attorney's intention to seek the death penalty. The majority remanded the issue for reconsideration on the merits of the notice issue. Judge Niemeyer dissented, concluding that there was no appellate jurisdiction.
I guess I'm missing something here, but I would have thought that the question of appealability would be resolved much in the same way as appeals based on violations of the Speedy Trial Act, which the U.S. Supreme Court has apparently cannot be taken pre-trial because the prejudice cannot be measured in advance. Somewhat similarly, I would have thought that the reasonableness or unreasonableness of the pre-trial notice would best be measured after the fact, when the parties could point to what actually happened at trial in arguing whether the timeliness of the notice was reasonable or not in its effect on the ability of the defendant to prepare for trial. (In other words, I think I'm with Judge Niemeyer.)