In keeping with tradition, I was able to find the answer in Emacs itself while asking this question.
It turns out the standard time functions work with different kinds of values:
Function arguments, e.g., the TIME argument to
accept a more-general "time value" format, which can be a list of
integers as above, or a single number for seconds since the epoch, or
nil for the current time. You can convert a time value into a
human-readable string using
format-time-string, into a list of integers using
and into other forms using
functions are described in the following sections.
seconds-to-time will do what's needed. Note that since
(current-time) returns microseconds as well – something not present in most UNIX timestamps – the assertion in the question won't hold as-written. If you strip microseconds from
(current-time), though, they'll be the same :-)