doc: specify unit of time passed to fs.utimes

PR-URL: #33230
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Anto Aravinth <anto.aravinth.cse@gmail.com>
Reviewed-By: Masashi Hirano <shisama07@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Juan José Arboleda <soyjuanarbol@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

Author: SimenB

doc/api/fs.md

@@ -3789,8 +3789,8 @@ Change the file system timestamps of the object referenced by `path`.
 
 The `atime` and `mtime` arguments follow these rules:
 
-* Values can be either numbers representing Unix epoch time, `Date`s, or a
-  numeric string like `'123456789.0'`.
+* Values can be either numbers representing Unix epoch time in seconds,
+  `Date`s, or a numeric string like `'123456789.0'`.
 * If the value can not be converted to a number, or is `NaN`, `Infinity` or
   `-Infinity`, an `Error` will be thrown.