When I do a man strftime, I get:

  The following conversion specifications are supported:
    %a     Replaced by the locale's abbreviated weekday
           name.
    %A     Replaced by the locale's full weekday name.
    %b     Replaced by the locale's abbreviated month
           name.
  ...

Maybe you just need to install better man pages? If you were doing a perldoc POSIX, I sympathize...

Update: To be fair, the POSIX perldoc contains the text:

  Consult your system's "strftime()" manpage for details
  about these and the other arguments.