I've recently found Gene Michael Stover's "Parsing Dates in Lisp" package.
It seems to answer the question of how to portably parse times in Lisp.
I'm working on adding support to LoGS to make better use of this. I want
to, amongst other things, have a command line option that causes LoGS to
use the timestamp as the value of *now* (without having to write some
funky user-level rule to do so (which is what I've done in the past,