offset-time deal with a calendar time datatype
which may or may not be disjoint from other Scheme datatypes.
Returns the time since 00:00:00 GMT, January 1, 1970, measured in seconds. Note that the reference time is different from the reference time for
get-universal-timein Common-Lisp Time.
Returns the difference (number of seconds) between twe calendar times: caltime1 - caltime0. caltime0 may also be a number.