strftime

Returns a string formatted according to the given $format string using the given $timestamp or the current local time if no timestamp is given. 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.