This is Sean Whalen (prion).
The delay of dawn was most likely caused by the ship of Tzadkiel being between the earth and the sun. Ossipago, Barbatus, and Famulimus could have given Tzadkiel the information that Severian needed some (subtle) help. Tzadkiel might have been able to learn this without the three's help, too.
In the back of the book, Gene's afterward section also says that it's possible that the natives just imagined that it was taking a long time to dawn because of being caught up in the force of Severian's narrative, or for other reasons.
prion