Php time and date format (strftime) to use in your php based CMS - There may be times where you need to specify a date format for your content or modules. 

The list below is what I have found for the php strftime acceptable formats.

PHP time and date format (strftime) a local time/date according to locale settings. Month and weekday names and other language dependent strings respect the current locale set with setlocale().

Not all conversion specifiers may be supported by your C library, in which case they will not be supported by PHP's strftime(). Additionally, not all platforms support negative timestamps, therefore your date range may be limited to no earlier than the Unix epoch. This means that e.g. %e, %T, %R and %D (there might be more) and dates prior to Jan 1, 1970 will not work on Windows, some Linux distributions, and a few other operating systems. For Windows systems a complete overview of supported conversion specifiers can be found at this » MSDN website.

• %a - abbreviated weekday name according to the current locale
• %A - full weekday name according to the current locale
• %b - abbreviated month name according to the current locale
• %B - full month name according to the current locale
• %c - preferred date and time representation for the current locale
• %C - century number (the year divided by 100 and truncated to an integer, range 00 to 99)
• %d - day of the month as a decimal number (range 01 to 31)
• %D - same as %m/%d/%y
• %e - day of the month as a decimal number, a single digit is preceded by a space (range ' 1' to '31')
• %g - like %G, but without the century.
• %G - The 4-digit year corresponding to the ISO week number (see %V). This has the same format and value as %Y, except that if the ISO week number belongs to the previous or next year, that year is used instead.
• %h - same as %b
• %H - hour as a decimal number using a 24-hour clock (range 00 to 23)
• %I - hour as a decimal number using a 12-hour clock (range 01 to 12)
• %j - day of the year as a decimal number (range 001 to 366)
• %m - month as a decimal number (range 01 to 12)
• %M - minute as a decimal number
• %n - newline character
• %p - either `am' or `pm' according to the given time value, or the corresponding strings for the current locale
• %r - time in a.m. and p.m. notation
• %R - time in 24 hour notation
• %S - second as a decimal number
• %t - tab character
• %T - current time, equal to %H:%M:%S
• %u - weekday as a decimal number [1,7], with 1 representing Monday
• %U - week number of the current year as a decimal number, starting with the first Sunday as the first day of the first week
• %V - The ISO 8601:1988 week number of the current year as a decimal number, range 01 to 53, where week 1 is the first week that has at least 4 days in the current year, and with Monday as the first day of the week. (Use %G or %g for the year component that corresponds to the week number for the specified timestamp.)
• %W - week number of the current year as a decimal number, starting with the first Monday as the first day of the first week
• %w - day of the week as a decimal, Sunday being 0
• %x - preferred date representation for the current locale without the time
• %X - preferred time representation for the current locale without the date
• %y - year as a decimal number without a century (range 00 to 99)
• %Y - year as a decimal number including the century
• %Z or %z - time zone offset or name or abbreviation (Operating System dependent)
• %% - a literal `%' character

Maximum length of this parameter is 1023 characters.