The reason that POSIX manual doesn't show the list of escape sequences is that the list depends on your OS. Perhaps you should make it more clear that your program is only of use for Windows users - on my system, I also have:

• %C: Century number (2 digits)
• %D: equivalent to %m/%d/%y
• %e: like %e, leading zero of month replaced with space
• %E: Modifier alternative format
• %F: Equivalent to %Y-%m-%d
• %g: Like %G, but use 2-digit year
• %G: 4 digit year, but if ISO week belongs to previous year, use previous year.
• %g: Like %G, but use 2-digit year
• %h: Equivalent to %b
• %k: Hours, 0 - 23, single digits preceeded by blank
• %l: Hours, 1 - 12, single digits preceeded by blank
• %n: Newline
• %O: Modifier alternative format
• %P: As %p, but in lowercase
• %r: Equivalent to '%I:%M:%S %p'
• %R: Equivalent to '%H:%M'
• %s: Number of seconds since epoch
• %t: Tab character
• %T: Equivalent to '%H:%M:%S'.
• %u: Day of week, 1 (Monday) - 7 (Sunday)
• %V: ISO week number of the year (01 - 53)
• %z: Time zone as offset of GMT.
• %%: A % character
• %+: Time in 'date' format

Here's a program to see what's available on your OS:

#!/usr/bin/perl

use strict;
use warnings;

use POSIX;

foreach my $ch ('a' .. 'z', '%', '+') {
    my $lc = strftime "%\l$ch", localtime;
    my $uc = strftime "%\u$ch", localtime;

    for ($lc, $uc) {
        s/\n/\\n/g;
        s/\t/\\t/g;
    }

    printf "%%%s  %25s   %25s\n", lc $ch, $lc, $uc;
}
__END__
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