Okay, I think *I* reproduced it.

1) I pulled your cpython350 fork down locally.

2) I updated to your checkin that fixed the bug. (c31dad22c80d)

3) I reverted the change to Modules/timemodule.c to put the bug back:
   % hg cat -r 97393 Modules/timemodule.c > Modules/timemodule.c

4) I changed line 611 (or so) from "#if defined(MS_WINDOWS) && !defined(HAVE_WCSFTIME)" to "#if 1" so I'd get the code that had the bug.

5) I ran "./configure --with-valgrind && make" to make it.

6) I ran "valgrind ./python -m test test_time" and ***Valgrind complained about an array overrun***.

7) I restored the bugfix to Modules/timemodule.c, then reinstated the change from 4) above.

8) I ran make and valgrind again and didn't get the complaint about the array overrun.

For grins I also tried enabling the other stanza of code that has the bug (the AIX / sun / have_wcsftime) and observed the same thing.

Is that convincing?