"The Boat of Millions of Years"

The above phrase on the opening page of Tim Powers' The Anubis Gates links this book with the title of Poul Anderson's The Boat Of A Million Years as we have previously said here. Anderson's novel features slower-than-light interstellar travel by a small group of immortals whereas Powers refers directly to Egyptian mythology:

"'...the twelve hours of the night...

"'It's the course through the Tuaut, the underworld, that the dead sungod Ra follows every night on his dark voyage from sunset to sunrise. Darkness becomes solid there, and hours are a measurement of distance, like sailing on an uncoiled clock face.'"

-The Anubis Gates, 10, p. 337.

Hours as distance: travel through time. Doyle replies that he has already travelled along such a river. 

Time as a river is a major image in Poul Anderson's Time Patrol series. See The River Of Time. Ra makes a big appearance in Neil Gaiman's The Sandman.