%{format}t	The time, in the form given by format, which should be in an extended strftime(3) format (potentially localized). If the format starts with begin: (default) the time is taken at the beginning of the request processing. If it starts with end: it is the time when the log entry gets written, close to the end of the request processing. In addition to the formats supported by strftime(3), the following format tokens are supported:
sec	number of seconds since the Epoch
msec	number of milliseconds since the Epoch
usec	number of microseconds since the Epoch
msec_frac	millisecond fraction
usec_frac	microsecond fraction
These tokens can not be combined with each other or strftime(3) formatting in the same format string. You can use multiple %{format}t tokens instead.