To answer my own question...
The self-test (in test.scm) for the built-in time package is
basically a sanity check on the current time (expressed as seconds
since Jan 1, 1970, the UNIX system base time):
(let* ((range-lo (string->bignum "1168000000"))
(range-hi (string->bignum "1200000000"))
(s start-time))
(if (not (and (bignum>= s range-lo) (bignum<= s range-hi)))
(failed `(and (bignum>= ,s ,range-lo) (bignum<= ,s ,range-hi)))))
...which doesn't seem to play very well with the current time:
% date +%s
1201357774
Looks like we're about 15.71 days past snow's expiration date. :-)
So I changed mine to "1210000000", which is good for another 3.17
years and I'm off and running.
Derrell