Heinlein made me think about it:
...had all been in that waterproof money belt Janet had given me so many light-years ago;...1Did he mean distance? It was in Canada (sort of) that she received the belt, now she just climbed out of the Mississippi river. That's a far distance. Or does did he mean time? Because the phraseology would be consistent with an expression of time. In which case he is wrong. But, hey, it's Heinlein! He knows his stuff! I'm sure he meant distance!
But check this out:
Flash back!! Back to a moment of time so many light years ago.2That is just not going to cut it. And from a dean at the University of New England, too!
For more information, check out the Light Year article at eSky.
1 Heinlein, Robert A. Friday New York: Holt Rinehart Winston, c1982. pg. 174.
2 Dean Kelley. "University of New England - COM - RSAS - Newsletter - September 2007 - Page 1". [Online](10April2009). URL: http://www.une.edu/com/rsas/newsletter/sept07a.asp