@defun time-subtract t1 t2
This returns the time difference @var{t1} @minus{} @var{t2} between
-two time values, normally as a Lisp timestamp but as a float
-if either argument is infinite or a NaN@.
-When the result is a timestamp, it is exact and its clock
+two time values, as a Lisp time value. The result is exact and its clock
resolution is no worse than the worse of its two arguments' resolutions.
+The result is floating-point only if it is infinite or a NaN.
If you need the difference in units
of elapsed seconds, you can convert it with @code{time-convert} or
@code{float-time}. @xref{Time Conversion}.