Here's a hilarious bit from Superman #170:
Um, that's quite a clock; each hour represents a billion years? And there are no smaller hands? If we accept that the clock is broken down into tenths or so, that still means 100 million years between each tick. In other words, there is no sense building any kind of mechanism to count the time; the clock might as well be a painted hand on a cave wall.
I had always remembered this particular story as imaginary, but reading it now, I realize that the only "imaginary" sequences are when Luthor fantasizes about his future as Superman's father. Luthor came within a moment or two of marrying Lara, but once he was gone, she quickly fell into the arms of Jor-El. Pretty lousy characterization!