Módulo do Apache mod_log_config :
%{format}t The time, in the form given by format, which should be in strftime(3) format. (potentially localized)
Exemplo:
LogFormat "%v %h %l %u %{%s}t \"%r\" %>s %b" vhost_common
CustomLog /var/log/test vhost_common
Log:
127.0.1.1 127.0.0.1 - - 1309405372 "GET / HTTP/1.0" 200 177