Try 4, viz. 29 May 1865, 7 Sep 1867, 4 Jul 1868, and 25 Dec 1868.
Technically the indictment remained pending until dropped altogether the following February and Davis was a free man, pardoned for his crimes.
Technically, it ended 25 Dec 1868 - a pardon is absolute. And the alleged disability provide by the 14th was a nullity until Davis et al actually were elected to office - you can't have Bills of Attainder take effect before the action was to be committed. If Davis never ran for office, the provision would not have been applied, so trial for treason was very much a possibility, and as before, said disability could easily have been removed by congress, so the federal government could never use claim that provision as any hindrance to a trial that you allege was open and shut.
Davis could never run for office, even if he wanted to, because of the restrictions of the 14th Amendment. Trial was not a possibility because the provisions of the 14th Amendment did represent punishment for the actions of the southern leaders. And Congress did not remove the restriction, until they did then the provisions against double jeopardy did apply. The the 14th Amendment was indeed an open and shut case preventing prosecution of Davis for his crimes.