Document this as a new feature.

Author: serhiy-storchaka

Doc/library/logging.handlers.rst

@@ -402,7 +402,8 @@ timed intervals.
    rollover interval.
 
    When computing the next rollover time for the first time (when the handler
-   is created), the last modification time of an existing log file, or else
+   is created), the creation time (if supported by the OS and file system)
+   or the last modification of an existing log file, or else
    the current time, is used to compute when the next rotation will occur.
 
    If the *utc* argument is true, times in UTC will be used; otherwise
@@ -449,6 +450,10 @@ timed intervals.
    .. versionchanged:: 3.9
       The *errors* parameter was added.
 
+   .. versionchanged:: next
+      Use the creation time instead of the last modification time, if supported by the OS and file system.
+
+
    .. method:: doRollover()
 
       Does a rollover, as described above.

Doc/whatsnew/3.16.rst

@@ -102,6 +102,17 @@ lzma
   requires ``lzma`` 5.4.0 or newer while RISC-V requires 5.6.0 or newer.
   (Contributed by Chien Wong in :gh:`115988`.)
 
+logging
+-------
+
+* :class:`~logging.handlers.TimedRotatingFileHandler` now uses the creation
+  time instead of the last modification time of an existing log file as
+  the basis for the first rotation after handler creation, if supported by
+  the OS and file system.
+  This allows it to be used in short-running programs that start and end
+  before the rotation interval expires.
+  (Contributed by Iván Márton and Serhiy Storchaka in :gh:`84649`.)
+
 os
 --
 

Misc/NEWS.d/next/Library/2021-02-26-13-17-57.bpo-40469.yJHeQg.rst

@@ -1,6 +1,5 @@
-A bug has been fixed that made the ``TimedRotatingFileHandler`` use the
-MTIME attribute of the configured log file to to detect whether it has to be
-rotated yet or not. In cases when the file was changed within the rotation
-period the value of the MTIME was also updated to the current time and as a
-result the rotation never happened. The file creation time (CTIME) is used
-instead that makes the rotation file modification independent.
+:class:`~logging.handlers.TimedRotatingFileHandler` now uses the creation time
+instead of the last modification time of an existing log file as the basis
+for the first rotation after handler creation, if supported by the OS and file system.
+This allows it to be used in short-running programs that start and end before
+the rotation interval expires.