Logging the "wrong time" means one of the following:

1) The timezone file is not accessible (no file, no permission).
   Use strace to see what system call fails.

2) The file contains the wrong data. Use cmp(1) to find out
   if it differs from a good file.

3) The process has the wrong TZ environment. Specify the TZ in
   /etc/postfix/main.cf.
   import_environment = MAIL_CONFIG MAIL_DEBUG MAIL_LOGTAG TZ=XXX LANG=C

4) The process effective user or group id is not equal to the
   corresponding real id (setuid/setgid binary or ancestor process),
   and so the process scrubs TZ from its environment for security
   reasons. In this case, explicitly adding TZ=... in main.cf,
   as above will help.

   Typically, only postdrop(1) (which only logs unexpected errors)
   runs in this way.